Neuromuscular Disorders
B. Presenting clinical features
Table 20. Presenting features of neuromuscular diseases. | ||||||||||||||||||||||||||||||
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C. Abnormal muscle activity
1. Clonus: Repetitive unidirectional contraction of a muscle group.
2. Fasciculations: Random twitching of a muscle fiber group.
3. Fibrillations: Random single-fiber twitching.
4. Myotonia: Delayed muscle relaxation, often triggered by percussion. Worse in cold, improves with exercise.
5. Myokymia: Repetitive, undulating fasciculations.
D. Pulmonary function in neuromuscular dz
Characterized by decreased vital capacity (VC), hypercarbia. A bedside test of VC is to have the pt count aloud while maximally exhaling: normal >40. Consider intubating if <20, or for VC <18 mg/kg. Oxygen saturation monitors are not adequate tests, as desaturation may only occur late. For Pulmonary function test findings, see p. 219.
E. Amyotrophic lateral sclerosis (ALS)
1. H&P: Weakness without cognitive, sensory, or ANS dysfunction. Combination of upper and lower motor neuron signs. Often asymmetric onset, hand atrophy, foot drop, leg spasticity, bulbar sx, fasciculations, cramps. Ask about family history.
2. DDx: CIDP, other motor system atrophies (dystrophies, spinal muscular atrophy), cervical spinal cord injury, syringomyelia, MS, myasthenia, paraneoplastic syndrome, multifocal motor neuropathy with conduction block, heavy metal poisoning, HIV, HTLV, Lyme, diabetic amyotrophy, postpolio syndrome….
3. Tests:
a. Consider peripheral neuropathy workup: see p. 93.
b. EMG: Much denervation and reinnervation (fasciculations, fibrillations, polyphasic increase in amplitude of motor units, normal conduction speed).
c. Biopsy: Usually not indicated. Shows neurogenic atrophy.
4. Rx:
a. Riluzole (Rilutek): 50 mg PO bid. Slightly slows progression.
b. Supportive: E.g., splints, G-tube, ventilator, antispasmodics, control saliva….
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