NEURONAL

MUSCULAR

Examination

Examination

Distal weakness and atrophy predominate

Proximal weakness and atrophy predominate

Sensory abnormalities common

No sensory abnormalities

Fasciculations common with anterior horn cell degeneration, less often present with radiculopathy or peripheral neuropathy

No fasciculations

Hyperactive response of muscle to direct percussion

Decreased response to percussion; myotonic response to percussion in myotonias or hypothyroidism

Special studies

Special studies

EMG: fasciculations, fibrillations, giant potentials; slowed nerve conduction with demyelinating peripheral neurpathy

EMG: myotonic potentials (high frequency, low amplitude); decreased motor units in general; normal conduction velocity.

Neostigmine: increased fasciculation

No response to neostigmine

Muscle enzymes usually not increased in blood

Muscle enzymes (CPK most sensitive) usually not increased in active disease.

Biopsy: atrophy and degeneration of groups of muscle fibers (motor units); degeneration of nerve fibers occasionally seen.

Biopsy: diffuse, patchy atrophy and degeneration of muscle fibers; inflammatory infiltrates seen in active myositis

Sedimentation rate (ESR) normal in most

Sedimentation rate (ESR) elevated in some myositis