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Chapter 12 - Evaluation of the Patient with Weakness

Introduction

Weakness is a common presenting concern in neurology. This chapter will discuss the evaluation of the weak patient. It will build on the chapter on examination of the motor system (chapter 10) and will defer to the chapter on neuromuscular disorders (chapter 21) for detailed discussion of many of the conditions.

The evaluation of the patient complaining of weakness must proceed in an orderly fashion. In the history, it is important to determine exactly what the patient means by "weak"; what are the specific muscle groups that are weak; whether there are associated findings with the weakness; and what has been the timing of onset of the weakness. Additionally, family history, the presence or absence of systemic signs and symptoms and the association of the weakness with other symptoms (such as pain) are relevant. Additionally, information about exposure to medications or toxins and potential exposure to infectious agents may be relevant. The examination can be helpful in determining whether the weakness is of upper or lower motor neurons or whether disease of the myoneural junction or of the muscles is present. Specialized testing, such as laboratory tests and electrodiagnostic testing may be of use in confirming the level of damage and focusing on an etiologic diagnosis.

History

What does the patient mean by “weakness?” You many be surprised to find that the patient is using the term to denote something other than what you understand to be the meaning of the term. In neurologic practice, weakness means the loss of strength or power, manifesting in the inability to generate normal force. The complaint of "fatigue" or general lack of energy rarely results from disturbance of the neuromuscular system and is not what this chapter is about. These complaints are often part of more systemic disorders, and are a common end result of many diseases, including rheumatologic disorders, endocrine, infectious and neoplastic disorders, not to mention psychiatric conditions. Complaints of "fatigue" may result from such diverse processes as sleep disorders or chronic fatigue and fibromyalgia syndrome. Although complaints of "fatigue" are rarely due to neurologic disease, it can occur as a result of multiple sclerosis and Parkinson disease (although rarely without other evidence of the condition). Therefore, the first step in evaluation is to determine whether the patient is truly weak and the history can begin to address this issue.

Occasionally, patients with other disorders of the motor system, such as rigidity or incoordination, may describe themselves as being weak because they have difficulties in performing motor acts. In this context, weakness may simply be a surrogate term for motor abnormality. Therefore, it is critical to determine whether the patient has actually lost power in performing certain actions. Simple questions, such as whether the patient can rise from a chair without assistance or climb a step, or whether they can lift up a gallon of milk from the refrigerator may help in determining whether strength and power are actually lost. A more open-ended question such as "what could you do that you no longer can do" may be a very helpful question in patients who are aware of their situation.

Spatial distribution of weakness. The next question that history can begin to answer relates to the particular pattern of weakness. For example, is the weakness mostly of proximal muscles or is it predominantly of distal muscles? Is the weakness on one side of the body or both and is it in the distribution of a particular nerve or group of nerves? Broad areas of weakness are more likely to be either damage to the central nervous system or a systemic disease that is attacking nerves. Weakness of a single limb can result from a large range of conditions, including spinal cord or multiple nerve roots, versus plexus lesions. Weakness of proximal muscles, that is weakness of shoulder and hip girdle muscles, is suggestive of a myopathic process (a process directly damaging muscles), while distal weakness is more likely to be a generalized polyneuropathy. If weakness of a limb is associated with lower facial weakness on the same side, the problem is above the brainstem, while if there is weakness of muscles on one side of the head and opposite limb, then a lesion in the brainstem is suggested.

Associated symptoms. Certain associated symptoms may help localize the part of the nervous system that is damaged, while other symptoms may put the condition in the larger context of disease. For example, the presence or absence of associated atrophy or fasciculations suggest damage to anterior horn cells or motor axons (i.e., lower motor neurons). Of course, any such report by the patient should be confirmed by examination. The presence of symptoms of systemic diseases may be a critical clue to diagnosis. For example, certain rheumatologic disorders can attack peripheral nerves. Several endocrine disorders, particularly those affecting thyroid or adrenal function, can present with weakness, while metabolic disorders such as diabetes mellitus often damage nerves. Hints regarding the presence of underlying neoplasia or infectious disorders may also be obtained from history.

Associated symptoms may provide important clues to whether other portions of the nervous system have been effected in addition to motor damage. Complaints of “numbness” or tingling, vision disturbance or vertigo suggest broader damage to the nervous system. The presence of such symptoms may indicate the level of damage to the nervous system or alert you to the presence of a neurologic syndrome. A change in character of the voice or problems swallowing (usually choking on water) suggests that the weakness may involve the pharyngeal muscles or those of the palate. Myelopathy (damage to the spinal cord) often produces bilateral symptoms below a certain level on the body. This may be attended by urgency of bladder function. Another common feature of damage to spinal cord, or peripheral nerves for that matter, is the combination of sensory and motor complaints. Some complaints can indicate a potentially serious neurologic disorder requiring urgent action. This includes rapidly progressive weakness of both lower extremities, which can be due to acute myelopathy, compressive lesions of the cauda equina (“cauda equina syndrome”) or Guillain-Barre syndrome. In any of these cases urgent evaluation is appropriate due to the need for prompt treatment.

Temporal characteristics. The tempo of onset and progression of the weakness is important, as is the question of whether the weakness is intermittent. Certain conditions have clear timing of onset and rapid progression. These include most vascular, infectious, inflammatory or traumatic disorders. Most degenerative conditions or those related with chronic conditions (such as metabolic or hereditary disease) develop insidiously. When conditions are intermittent, it is important to determine whether there are particular things that precipitate or worsen it. For example, if repeated activity tends to worsen the weakness (for example, if there are things that patients can’t do at the end of the repeated activity that they could at the beginning), this suggests a diagnosis of myasthenia gravis (a neuromuscular disease). If there are particular movements or postures that results in the weakness, this suggests some mechanical or orthopedic problem such as entrapment neuropathy, radiculopathy or localized vascular occlusive problem. If there are particular times of the day that symptoms are present, or if there are definite associations with eating, an ion channel disorder should be considered. Finally, if the symptoms happen at random, with recovery after five to 30 minutes, transient ischemia of the central nervous system should be considered.

Family history. Family history may be important in detecting hereditary neuropathies and myopathies. Additionally, some of the familial periodic paralysis problems that are associated with ion channelopathies may be hereditary.

Pain. Pain can be a particularly difficult symptom to assess in the weak patient. First of all, a highly specific pain pattern may indicate nerve root damage or damage to a particular peripheral nerve. On the other hand, many patients with pain report “weakness” that has nothing to do with nervous system damage. There are both voluntary mechanisms and unconscious mechanisms that limit the use of a painful body part. This can be perceived by the patient as weakness, despite a completely normal and intact neural and neuromuscular mechanism. On examination of such patients, there appears to be intermittent effort and “break-away” type weakness and the patient may be perceived to be “faking it.” This assessment should be made with great caution, especially in the case of painful syndromes.

Examination of the weak patient

Once the history has been obtained, the examination is focused on confirming the pattern of weakness and determining the type of weakness. True weakness can be caused by problems affecting upper motor neurons, lower motor neurons, the neuromuscular junction or the muscle itself. Upper motor neurons represent the neurons in the brain, whose axons descend the brain stem and spinal cord to contact the anterior horn cells. In practice, many of these are corticospinal (pyramidal) neurons. In many ways, these can be thought of as the "command neurons” for movement. The lower motor neurons are the anterior horn cells, along with their axons. These axons course through the ventral root, plexi and peripheral nerves, in order to reach their targets in the muscles. The myoneural junction is the cholinergic synapse between the lower motor neurons and muscle fibers, which represent the final contractile element.

Upper motor neuron. Upper motor neuron weakness presents in a rather characteristic pattern. First of all, it tends to affect broad areas of the body. This is because axons are quite tightly packed when they are in the brain stem and spinal cord. Typically, weakness is accompanied by an increase in deep tendon reflexes such as the biceps, triceps, patellar or ankle jerks. There is usually a decrease in superficial reflexes such as the abdominal, cremasteric reflex or the normal plantar response. There may well be the appearance of pathological responses, such as the Babinski response. Finally, upper motor neuron lesions are characterized by relatively minimal atrophy, and do not lead to the fasciculations. It is noteworthy that some atrophy may take place of disuse nature, since the affected body part is unlikely to be exercised regularly. There may be increased tone of a spastic nature associated with heightened muscles stretch reflexes. This increased tone tends to appear in a "clasp knife" pattern. One caveat in the evaluation of upper motor neuron problems is that very large and acute injuries may produce a period of generally diminished tone and responses that has been termed "spinal cord shock" since this is usually seen with acute traumatic spinal cord injuries.

Lower motor neuron. Lower motor neuron weakness may result from damage to the anterior horn or its axon anywhere along its course from the CNS to the muscle that is weak. Lower motor neuron disease tends to result in decreased muscle tone, decreased reflexes in the affected area, atrophy and, possibly, fasciculations. Fasciculations are most prominent when the anterior horn cell is affected. They result from the random and spontaneous depolarization of a motor neuron or motor axon and results in a visible twitch of the skin over the muscle. Of course, there are benign fasciculations that most people have had at one time or another due to local irritation of motor nerve fibers in an overused muscle (these are temporary). Some individuals have more persistent benign fasciculations (usually in the calves). However, in the case of benign fasciculations the twitches are not associated with any other sign of lower motor neuron damage. Electromyography can be used to confirm this, if necessary.

Lower motor neuron damage within a peripheral nerve results in a distribution of symptoms that reflect of the motor distribution of the peripheral nerve (see table 10-5). The diseases that damage anterior horn cells are generally more widespread and do not follow the distribution of a single nerve (although they can focus on one limb, especially early in the course).

Neuromuscular disease. Neuromuscular disease is characterized by fluctuating strength based on muscle use. For example, myasthenia gravis results in decreasing power with continuous contraction. On the other hand, Lambert-Eaton myaesthetic syndrome (LEMS) results in increased strength with repeated contraction.

Myopathy. Muscle diseases are generally proximal and symmetrical. These often result in particular difficulties arising from the chair or holding up one's arm against gravity. There is usually minimal atrophy until late in the course and muscle stretch reflexes typically remain normal. An exception to this general rule is myotonic dystrophy, which tends to affect the muscle of the distal extremity most prominently. This condition is associated with myotonia, which is recognized by the inability to rapidly relax a muscle after tonic contraction (for example, problems opening the hand quickly after making a tight fist).

There are some unusual diseases that produce intermittent weakness of muscle contraction, most notably the familial periodic paralyses. These conditions are associated with abnormal ion channels and can be particularly difficult to diagnose. Patients often show abnormal serum potassium (some low and some high) during the episode of weakness and symptoms often follow a period of exercise or follow a heavy carbohydrate meal. Examination in between attacks may be completely normal until late the condition.

Laboratory testing

Various laboratory tests may aid in diagnosis. If peripheral nerve disease is anticipated, testing of complete blood count, glucose level, sedimentation rate, serum protein electrophoresis, antinuclear antibody levels, VDRL/RPR, vitamin B12 level, and Lyme titer may be useful. In the right setting, testing of heavy metal exposure, or firms or HIV status may be appropriate. Muscle disease often results in an increase in creatine kinase levels in the blood, although this is quite nonspecific in terms of etiologic diagnosis.

Blood tests for antibodies against acetylcholine receptors or certain other muscular antigens may be indicated when neuromuscular disease is suspected. These are not 100% sensitive, however.

When the location or distribution of weakness is in question, electromyography and nerve conduction studies may be extremely helpful (See the discussion on electrodiagnosis). This testing is particularly good at identifying signs of damage of nerves to muscle and nerve conduction studies often localize the specific point of nerve injury. Needle electromyography is the single most sensitive test at detecting lower motor neuron damage and may give important information as to whether this is recent or old. Newer techniques, such as transcranial cortical magnetic stimulation, may effectively examine the central motor pathways, as well.

Neuromuscular disease can also be studied electrodiagnostic testing. Repeated nerve stimulation may either show a decrease with repetition (myasthenia gravis) or an increase in contraction (LEMS). While these are not very sensitive tests, they are quite specific. Single fiber electromyography is a highly specialized procedure, but increases the sensitivity of electrodiagnostic testing for suspected neuromuscular disease

Causes of weakness

There are many potential causes of weakness. Each of these conditions is explained in greater detail in the third section of the book and we will only briefly touch on the differential diagnosis once a decision has been made as to whether the weakness is due to damage to upper motor neurons, lower motor neurons, the neuromuscular junction or the muscle.

Muscle diseases. Muscle diseases are most often productive of proximal and symmetrical weakness. As described in the previous section, there may be EMG abnormalities and creatine kinase levels are often elevated. Some of these conditions are primary, with the pathologic process essentially restricted to the muscle, and some secondary, where the muscle is affected by the systemic disease. The finding of a secondary myopathy often leads to a specific treatment, so it is important to consider these early in the evaluation. Causes of secondary myopathy include: infection (such as trichanosis), connective tissue disease, endocrine abnormality (particularly thyroid and adrenal dysfunction), paraneoplastic processes or may be related to drug or toxin exposures (for example statins). Primary myopathies can be broadly broken into subcategories of congenital or hereditary myopathies (dystrophies), inflammatory myopathies, and metabolic myopathies. These are discussed in greater detail in chapter 21. The inflammatory myopathies are occasionally recognized by systemic signs, along with blood chemistry findings of muscle damage and inflammation (although inclusion body myositis may be insidious and without these other features). The dystrophies and metabolic myopathies (which are due to some deficit in critical muscle enzymes) tend to be more slowly progressive and often require invasive and specific genetic testing for confirmation. Table 21-5 lists conditions that should be considered in the differential diagnosis of myopathy.

Neuromuscular junction. Neuromuscular junction disorders may result from drugs and toxins or from diseases such as myasthenia gravis or Lambert-Eaton myaesthenic syndrome. Toxins such as botulinum toxin, certain snake venom's or tick-borne toxins are rare, but enter the differential diagnosis of neuromuscular disease. Drugs that affect neuromuscular transmission or certain pesticides can work in a similar way to block neuromuscular transmission. However, myasthenia gravis, and LEMS represent the majority of potential causes of neuromuscular conduction blockade. These are described in some detail elsewhere in the book. Briefly, myasthenia gravis, produces a decrement in strength with continued contraction, and most commonly affects the muscles of the eye and pharynx. Lambert-Eaton myasthenic syndrome, which typically affects hip girdle mussels, results in increased strength following repeated contraction.

Lower motor neuron. Lower motor neuron problems may result from several processes, including those affecting peripheral nerves, plexi, nerve roots or the anterior horn cells in the brainstem and spinal cord. Polyneuropathy results from a systemic condition damaging peripheral nerve. This may be due to toxic, metabolic, nutritional, infectious, hereditary, or immune/inflammatory conditions. The diagnosis of the patient with polyneuropathy is discussed in chapter 21 although most of the potential causes are listed in table 21-4. One particularly important condition producing polyneuropathy is acute inflammatory demyelinating polyradiculoneuropathy (AIDP; Guillain-Barré syndrome). This condition should be considered in any patient with acute or subacute progression of weakness with loss of reflexes. A waxing and waning, chronic form of inflammatory polyradiculoneuropathy also exists (CIDP).

Many cause of lower motor neuron symptoms are due to local compression or trauma to nerves or nerve roots. These are recognized by the pattern of weakness (table 10-5). Compressive neuropathies and traumatic injuries tend to occur at specific sites along the peripheral nerves (see: Chapter 21)

Radiculopathy usually results from conditions in and around the spine, including intervertebral disc disease, spinal stenosis, neoplasms, radiation or chronic forms of meningitis can damage peripheral nerve roots either singularly or multiply (polyradiculopathy). These are often recognized as producing radiculopathic pain, which is frequently, though not always, provoked by particular movements or positions (such as the straight leg raise or Spurling’s maneuver (fig 1-4; fig 1-5).

Anterior horn cell disease typically produces significant fasciculations and atrophy. These conditions are usually degenerative, traumatic or infectious, though occasionally other casues of damage to the spinal cord (such as neoplasms, radiation or vascular insufficiency) can present with amyotrophy. Degenerative conditions include a range of conditions, generically termed “motor neuron diseases.” The prototype for the family of conditions is amyotrophic lateral sclerosis. Infections can also damage the anterior horn cells. The prototype for these conditions is poliomyelitis. However, a range of infectious processes, including cytomegalovirus and Lyme disease, may also attack the anterior horn cell and result in lower motor neuron damage. Compressive disorders of the spinal cord, whether chronic and due to degenerative spinal stenosis or subacute (such as with tumors or mass lesions) can preferentially affect the gray matter of the spinal cord and produce anterior horn cell damage. Spinal cord radiation, vascular occlusive disease in the spinal cord (quite rare) or infiltrating tumors of the spinal cord (also quite rare) are additional considerations. Fortunately, magnetic resonance imaging has made the evaluation of expensive segments of the spinal cord much easier.

Upper motor neuron disease. Finally, a finding that weakness results from upper motor neuron damage requires consideration of all disorders that can damage the cerebral cortex or axons extending through the brainstem and spinal cord. These include cerebrovascular disease, vascular malformations, tumors, trauma, infection, demyelination, degenerative conditions, congenital problems, toxic disorders, metabolic disorders, developmental problems or radiation damage.

Summary

In summary, the evaluation of the weak patient needs to be systematic. History can help determine whether the patient is truly weak, and the pattern of weakness. It can also help determine whether hereditary disorders or other associated metabolic or endocrine conditions are high on the list of possibilities. Medications and toxic potential toxic exposures should be explored as part of the history and an understanding of the tempo of the condition must be obtained. Examination is focused on helping to determine whether the weakness is likely to result from upper motor neuron problems, lower motor neuron problems, myoneural junction problems or myopathy. Electromyographic studies may be useful in confirming the impression of neuropathy, anterior horn cell disease or myoneural junction disorder. Blood tests may aid in ascertaining a cause. Finally, narrowing down the cause of the weakness requires considering the list of possible conditions that can produce the type of weakness being manifested by the patient.

Reference

Questions

Define the following terms:

fatigue, rigidity, myopathy, neuromuscular junction/myoneural disease, upper motor neuron, lower motor neurons, polyneuropathy, Charcot-Marie Tooth, Lambert-Eaton myasthenic syndrome, paraneoplastic syndrome, myasthenia gravis, nerve conduction study, electromyography.
Fatigue, from a neurologic perspective, means a decrease in the ability to exert force with repeated or sustained contractions of a muscle. This usually results from disease of the neuromuscular junction. However, laypeople almost never mean this when they use the term "fatigue."
Rigidity refers to a stiffness (increased muscle tone) that produced a smooth resistance to passive movement throughout the range of a passive movement. This is due to extrapyramidal disease, usually Parkinson disease.
Myopathy is a condition that damages muscles diffusely. These are either primary muscle disease or are secondary to some systemic problem. The primary diseases are due to familial (usually metabolic) disease, muscular dystrophies or inflammatory conditions of muscle. The secondary myopathies are usually toxic, endocrinological or infectious.
Neuromuscular junction (myoneural) disease is a condition that is damaging the neuromuscular junction at the motor end-plate on muscles.
"Upper motor neuron" refers to the motor control neurons in the cerebral cortex and brain stem that give rise to descending pathwyas innervating motor neurons.
Lower motor neurons are the anterior horn cells and their axons that innervate muscle fibers. These axons traverse nerve roots, plexi and the peripheral nerves in their course to the myoneural junction.
Polyneuropathy is generalized damage to peripheral nerves. The conditions that cause this are usually systemic (toxic, nutritional deficiency, autoimmune, endocrinolgic, metabolic, hereditary) and affect the longest nerve first. The symtptoms are almost always seen in the feet first.
Charcot-Marie Tooth is a group of hereditary neuropathies that usually begin to show clinical signs in late childhood and adolescence and progress slowly. It notably affects muscles of the feet and calves early in the course.
Lambert-Eaton myasthenic syndrome is an autoimmune (and often paraneoplastic) condition that produces weakness, usually of hip girdle muscles.
A paraneoplastic syndrome refers to remote effects of a tumor. Most often it represents a condition in which antibodies directed at a tumor damage otheer tissues of the body.
Myasthenia gravis is a conditon in which there is antibody-mediated destruction of the acetylcholine receptors producing weakness and fatigability of muscle.
A nerve conduction study is a test of speed and amplitude of conduction of peripheral nerve fibers.
Electromyography is a needle study in which the electrical activity of muscle fibers is recorded. It can detect damage to muscles and is sensitive to muscle fibers that have been disconnected from their nerves (denervated).

12-1. What are the levels of the nervous system that can produce true weakness?

Answer 12-1. Upper motor neurons (descending tracts of the central nervous system); lower motor neurons (the anterior horn cell and the axons traveling through the peripheral nerve to the muscle); the neuromuscular junction; the muscle.

12-2. How is strength graded?

Answer 12-2. A 5 point scale, with 5 being normal, 4 being weak, 3 being only strong enough to move against gravity and no additional resistance, 2 being unable to move against gravity and 1 being a flicker of contraction of the muscle by no actual limb movement of any kind.

12-3. How can strength be tested functionally?

Answer 12-3. The patient can attempt to hold the arms out in front, with weakness of the whole upper limb reflecting in pronator drift. Grip can be tested by squeezing of two of the examiner’s fingers. Making an “OK” sign with the thumb and index finger tests the thenar muscles. Abduction and adduction of the ulnar 4 digits tests interosseous and hypothenar muscles. Walking on the toes and heels, climbing a small step, hopping on one foot or rising from a chair tests lower extremity muscles.

12-4. Other than actual weakness, what other symptoms might the patient be describing when they use the term “weak”?

Answer 12-4. Most motor problems can be described as “weakness.” These include rigidity or incoordination (possibly due to extrapyramidal or cerebellar disease, respectively).

12-5. What is suggested by proximal, symmetrical distribution of weakness (hip and shoulder girdle)?

Answer 12-5. This is the pattern most often seen in a myopathic process.

12-6. What is suggested by distal, symmetrical distribution of weakness (feet and/or hands)?

Answer 12-6. This is the pattern most often seen in a neuropathic process.

12-7. What does it mean if there atrophy out of proportion to the degree of disuse?

Answer 12-7. This indicates lower motor neuron lesion.

12-8. What would be suggested by fatigability of muscles?

Answer 12-8. Neuromuscular diseases, such as myasthenia gravis, can produce fatigue of muscles. Remember, we are discussing the actual loss of strength with continued muscle contraction, not the symptoms that most patients call “fatigue.”

12-9. What conditions can cause transient weakness?

Answer 12-9. Transient ischemic attacks, neuromuscular diseases (like myasthenia), peripheral nerve entrapment problems, the periodic paralysis family of conditions or, rarely, migraine can cause transient weakness. Patients can also be transiently weak after a seizure (Todd paralysis).

12-10. What is suggested by a story of severe, global weakness associated with heavy meals or periods of exercise?

Answer 12-10. This is a story suggestive of one of the periodic paralyses (an ion channelopathy). There may be a family history of similar problems.

12-11. What systemic conditions can produce weakness?

Answer 12-11. Thyroid or adrenal dysfunction and certain rheumatologic/inflammatory conditions can lead to muscle damage (myopathy). Many systemic problems can lead to polyneuropathy (generalized damage to peripheral nerve). Also, diabetes mellitus, hypertension and dyslipidemas predispose to cerebrovascular disease, which can damage upper motor neurons.

12-12. How can pain affect the diagnosis of the patient with weakness?

Answer 12-12. Pain may be part of the condition (particularly those that damage nerves or muscle). Pain may also produce an unwillingness or even inability to use the body part.

12-13. What conditions can present as bilateral weakness of the lower limbs?

Answer 12-13. Myelopathy (damage or disease of the spinal cord) usually produces bilateral symptoms below a certain level, often with some bladder urgency (this may require urgent MRI scanning of the cord). Cauda equina compression (syndrome) is suggested by flaccid weakness of the legs, often with urinary retention or overflow incontinence. A progressive weakness of both legs, evolving over hours to days, is a presentation of Guillain-Barre syndrome (an acute demyelinating polyradiculoneuroapthy of an immune nature). Myopathic processes tend to affect the hip girdle muscles early and Lambert-Eaton myasthenic syndrome usually begins with proximal hip girdle muscle weakness.

12-14. What is the likely cause of weakness of one side of the body that is associated with a lower facial weakness on the same side?

Answer 12-14. The problem is with upper motor neurons above the level of the brainstem (usually cerebral cortex or internal capsule).

12-15. What is the likely cause of weakness of one side of the body that is associated with weakness on the opposite side of the head (tongue, jaw, palate or eyes)?

Answer 12-15. The damage is localized to the brain stem (usually the medial aspect).

12-16. What procedure can be used to objectively demonstrate whether nerves to a muscle are damaged?

Answer 12-16. EMG can determine whether lower motor neurons to a muscle are intact. The pattern of denervated muscles is then used to try to distinguish whether a single nerve is involved or whether this is due to damage to a nerve root or the nerve plexus.

12-17. What is the effect of upper motor neuron damage upon muscle bulk, tone, deep tendon reflexes and superficial reflexes?

Answer 12-17. Upper motor neuron damage generally produces increased deep tendon reflexes, along with diminished normal superficial reflexes and some pathological reflexes (such as Babinski)? Muscle tone is usually increased in a pattern of spasticity (clasp-knife).

12-18. What is the effect of lower motor neuron damage upon muscle bulk, tone, deep tendon reflexes and superficial reflexes?

Answer 12-18. Lower motor neuron damage generally produces decreased deep tendon reflexes in the effected area. Superficial reflexes are usually not effected unless the weakness is very severe. Muscle tone is usually decreased and there is often severe atrophy that develops over time. If the motor neuron itself is damaged, fasciculations are usually prominent.

12-19. What is the effect of muscle or neuromuscular disease on muscle bulk, tone, deep tendon reflexes and superficial reflexes?

Answer 12-19. Usually all of these are normal, although very late in muscular disease there may be atrophy.

12-20. What kinds of problems produce diffuse muscle damage (myopathy).

Answer 12-20. Problems with muscle include congenital/hereditary (muscular dystrophy, congenital myopathy),; infection (trichinosis); connective tissue disease (polymyositis, scleroderma, mixed connective tissue disorder); endocrine (hypo/hyperthyroid, hyperparathyroid, hypo/hyperadrenia); neoplastic; drug-induced (clofibrate, statins, corticosteroids).

12-21. What kinds of conditions damage or block the neuromuscular junction?

Answer 12-21. Problems with neuromuscular junction include: paraneoplastic (Lambert-Eaton Myasthenic syndrome); immunologic (Myasthenia gravis); toxins (botulism, snake venom, tick bite); drugs(antocholinesterase toxicity).

12-22. What differences would be expected between myasthenia gravis and Lambert-Eaton myasthenic syndrome (LEMS).

Answer 12-22. Myasthenia gravis causes progressive weakness during sustained or repeated contraction. This usually affects the eyes early (though it can primarily affect speech and swallowing or be generalized). LEMS patients usually get stronger with repetition. It tends to affect hip girdle muscles most prominently and tendon reflexes are usually diminished (and improve after exercise).

12-23. What is the effect of lower motor neuron damage upon muscle bulk, tone, deep tendon reflexes and superficial reflexes?

Answer 12-23. Lower motor neuron damage generally produces decreased deep tendon reflexes in the effected area. Superficial reflexes are usually not effected unless the weakness is very severe. Muscle tone is usually decreased and there is often severe atrophy that develops over time. If the motor neuron itself is damaged, fasciculations are usually prominent.

12-24. What disorders can damage peripheral nerves?

Answer 12-24. Problems with peripheral nerve include: trauma (including entrapment); toxins (lead, alcohol, several medicines); infections (diptheria, Lyme, HIV); Inflammatory (CIDP, Guillain-Barre); metabolic (diabetes, porphyria); vascular (autoimmune arteritis); nutritional (vitamin B1 or B12 deficit or pyridoxine toxicity); heredity (Charcot-Marie-Tooth disease, etc); neoplasm; abnormal proteins (amyloidosis).

12-25. What kinds of conditions damage nerve roots?

Answer 12-25. Problems with nerve root(s) include: intervertebral disk herniation; neoplasm; foraminal encroachment; radiation; toxins, chronic meningitis.

12-26. What kinds of conditions damage anterior horn cells?

Answer 12-26. Diseases directly damaging anterior horn cells include: infection (polio); spinal cord trauma; tumors; paraneoplastic; degenerative (ALS, progressive spinal muscular atrophy); disc (spondylotic myelopathy); radiation myelopathy; vascular.

12-27. What kinds of problems are associated with upper motor neuron damage?

Answer 12-27. Disorders associated with damage to upper motor neurons include: vascular (stroke/TIA, AVM); tumor; trauma; infection (transverse myelitis, HIV); demyelination (MS); degeneration (ALS, primary lateral sclerosis); congenital (cerebral palsy); toxic/anoxic; developmental (Chiari, spinal stenosis).
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