Page 354 - Motor Disorders Third Edition
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336 / chapter 17 termination sites on skin appendages or dermal blood ves-
Guillain-Barré syndrome (GBS) is an important cause of sels. Electron microscopy (EM) reveals tuberomembranous
and tuberocisternal profiles (29, 30). The accumulation of
acute ascending symmetric weakness, hypotonia, and are- this material in the axon terminal suggests impaired axonal
flexia of infancy (24). It leads to progressive proximal motor transport in infantile neuroaxonal dystrophy (30).
weakness of the legs, later followed by involvement of the
arms, trunk, and face. Areflexia is common although trace The causes of acute descending weakness may be due to a
reflexes of the biceps and knee jerk may be present. Eleva- disorder of the neuromuscular junction. Weakness and hypo-
tion of the CSF protein content with few or no cells, termed tonia due to botulism develop in a previously healthy infant
albuminocytologic dissociation, should be documented age two to six months, although cases have been described in
over several weeks (25). Electrophysiological studies reveal the first two weeks of life (31, 32). The weakness is caused by
reduced compound muscle action potential (CMAP) ingestion of Clostridium (C.) botulinum spores which germi-
amplitudes to 50% of normal with prolongation of F-wave nate in the infant gut and elaborate low levels of exotoxin. The
latencies even before the decrease in motor nerve conduc- toxin cleaves synaptobrevin, a membrane component of small
tion velocities (NCV), which are maximal by the third week synaptic vesicles, and impairs presynaptic axonal release of
of illness. Denervation potentials on needle EMG occur late ACh, thereby producing weakness (33). Electrophysiological
in the course and are associated with a poor outcome (26). studies show decreased miniature end-plate potentials due
Treatment involves supportive care and careful monitoring to a decrease in quantal release of ACh upon nerve terminal
of cardiac and respiratory status, and consideration of plas- depolarization (34). Clinical weakness typically begins with
mapheresis and/or intravenous immunoglobulin (IVIg) multiple cranial nerve palsies, leading to bilateral ptosis and
therapy. Diphtheria, caused by Corynebacterium diphthe- dilated pupils with diminished light response. Poor feeding
ria, produces a generalized demyelinating polyneuropathy is due to decreased suck ability and pooling of secretions in
clinically similar to GBS. A protein exotoxin secreted by the pharynx. The weakness descends to the trunk and limbs;
the organism inhibits myelin synthesis activates cytotoxic bowel sounds are hypoactive, and constipation is common.
mechanisms. Treatment consists of anti-toxin administra- Deterioration can be rapid and lead to progressive respira-
tion and antimicrobial therapy. Tick paralysis is an acute ill- tory compromise requiring ventilator support (35). The most
ness similar to GBS that presents in the spring and summer specific single electrophysiological test for botulism is an
months with hypotonia caused by tick attachment that leads incremental response on repetitive motor nerve stimulation
to the secretion of neurotoxinladen saliva; prompt removal at 20 to 50 Hz. Concentric-needle EMG shows short-dura-
of the tick is rapidly curative (27). Subacute and chronic tion low-amplitude motor unit potentials (MUP) (34). Fecal
diffuse neuropathies that cause hypotonia include meta- material should be sent for culture of C. botulinum and for
chromatic leukodystrophy (MLD), globoid cell leukodys- exotoxin identification. Environmental cultures, including
trophy or Krabbe disease, neonatal adrenoleukodystrophy soil and dirt samples from the home, honey, or other prod-
(ALD), and infantile neuroaxonal dystrophy. Clues to their ucts that may have been fed to the infant, are sometimes pos-
diagnosis may include a known family history, UMN signs, itive, suggesting the specific source of infection. Most infant
CSF protein elevation, and slow nerve NCV. Metachromatic botulism in the United States is caused by group I organisms
leukodystrophy, globoid cell leukodystrophy, and adreno- that elaborate toxin types A and B. Treatment of infantile
leukodystrophy all demonstrate white matter abnormalities botulism is supportive, but prompt treatment with Botu-
on cranial magnetic resonance imaging (MRI). In neona- lism Immune Globulin Intravenous (human) (BIG-IV) may
tal adrenoleukodystrophy, moderate to severe hypotonia reduce the length of hospital stay (31). Attention should be
hepatomegaly and retinitis pigmentosa are noted at birth paid to avoiding any medications that might exacerbate the
or shortly thereafter. Increased plasma levels of very-long- neuromuscular transmission deficit, in particular aminogly-
chain fatty acids are found, often with raised phytanic acid coside antibiotics, which are sometimes initiated empirically
and bile fluid trihydrocoprostanic acid levels, consistent with at presentation for possible sepsis (32). Autonomic nervous
a deficiency of multiple peroxisomal enzymes (28). Infantile system (ANS) dysfunction, especially with regard to cardio-
neuroaxonal dystrophy is an AR disease, with marked gener- vascular responses, occurs in some infants with severe botu-
alized hypotonia in late infancy. There is an overall regression lism and may persist beyond objective motor deficits (33).
of motor and language milestones, which may be accompa- Full recovery is expected but may require several weeks to
nied by bilateral pyramidal signs, esotropia, and pendular months. The congenital myasthenic syndromes are a het-
nystagmus. Electroencephalography (EEG) demonstrates erogeneous group of rare conditions caused by a variety of
an admixture of high-amplitude 18- to 20-Hz beta activity. genetic defects affecting neuromuscular transmission (36).
Cranial MRI, electrophysiology studies, and serum amino Unlike neonatal and juvenile myasthenia gravis, they are
acid screens are generally all normal (29). The diagnosis can not antibody mediated. Affected children manifest weakness
be ascertained on skin and conjunctival biopsy, where axo- and abnormal fatigability on exertion in the first two years
nal spheroids are found in unmyelinated nerve fibers near
