This chapter summarizes neuromuscular diseases that affect the skeleton as a result of pathologic conditions of the spinal cord or peripheral nervous system. These diseases may present a fully developed picture or show early subtle findings, such as a mild deviation of gait. The tables in this chapter organize the neuromuscular diseases according to the location of pathology reference.

Evaluation

The elements of evaluation of neuromuscular disease include the following:

1. History: Prenatal, birth (gestation, weight, apgar scores), developmental (milestones), family

2. Physical examination

a. Motor strength, tone

b. Deep tendon reflexes

c. Cranial nerves

d. Cerebellar signs

3. Serum creatine phosphokinase (CPK)

a. Elevation directly related to amount of muscle necrosis or membrane disorder. Abnormal in Duchenne and Becker muscular dystrophies (>20 times normal in childhood and early teens), myopathies, or myositis

b. Minimal to mild elevation in other dystrophies

4. Immunocytochemistry: Directly differentiates Duchenne from Becker dystrophies and other conditions. Requires small amount of muscle tissue

5. DNA mutation analysis: Requires small amount of blood or amniotic fluid, allows prenatal diagnosis

6. Electromyelography (EMG): Distinguishes myophatic from neuropathic weakness

a. Myopathic process: Polyphasic low-voltage signal; fibrillations and sharpwaves

b. Neuropathic process: Initially, brief biphasic low-voltage fibrillation

c. Chronic process: Prolonged polyphasic fibrillation, increased amplitude

a. Abnormally slowed conduction velocities in conditions involving peripheral nerves only

b. Normal conduction velocities in spinal muscular atrophy

c. Normal conduction velocity (>49 m/s in arms, >39 m/s in legs) for patients over 5 years of age. Younger children have slower conduction velocity.

8. Muscle biopsy: Biopsy minimally involved muscle in chronic conditions and severely involved muscle in acute conditions. Vastus lateralis used for proximal myopathy, should be done only in centers capable of doing special histochemistry

a. Type I fibers: Oxidative metabolism, slow twitch

b. Type II fibers: Anaerobic metabolism, fast twitch

c. Myopathic process Necrosis, phagocytosis, and inflammation Irregularly sized fibers Type I predominance less than 50%

d. Neuropathic process Small group atrophy Fiber-type grouping, angular fibers Type II predominance greater than 80%

e. Electron microscopy (glutaraldehyde) is used to differentiate architectual changes within the congenital myopathies

9. Nerve biopsy

a. Sural nerve most commonly biopsied

b.