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Genetic disorder characterized by bilateral sensorineural
deafness and variable but progressive cranial and spinal motor nerve
involvement.
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Pontobulbar Palsy with Deafness; Progressive Bulbar Palsy
with Perceptive Deafness; Progressive Bulbar Palsy with Sensorineural
Deafness.
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Unknown, but more than 30 cases have been reported in the literature
with an unconfirmed number of affected siblings and relatives.
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Originally thought to be autosomal recessive transmitted,
but later suggested to be genetically heterogeneous with autosomal recessive
and dominant transmission or the result of a mutant gene carried on the
X-chromosome. Both familial and sporadic cases have been reported.
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Muscle biopsy sections demonstrate atrophic fibers
scattered equally between type I and II fibers. Histologically, silver
staining shows loss of axons in intravascular nerve bundles. Sural nerve
biopsy shows a depletion of nerve fibers and fibrosis in the perineurium.
Electron microscopy reveals nonspecific changes characteristic of denervated
muscle fibers. Cranial nerves and nuclei show a marked loss of both myelin and
axons with gliosis. Electrophysiologic testing of affected muscle groups
shows widespread and symmetrical denervation at the level of the lower motor
neuron suggesting a pathologic process affecting the motor neuron or
proximal part of the motor nerve roots. An upper motor neuron component was
also detected in certain muscle groups.
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Characteristic clinical findings, clinical course,
electrophysiologic testing, muscle and nerve biopsy, and histopathologic
analysis.
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The onset is usually in childhood, and the course
tends to be irregularly progressive. The presenting symptom is usually a
perceptive hearing loss caused by bilateral sensorineural deafness of slow or rapid
onset. This is followed by signs of lower cranial nerve motor palsies.
Intercurrent illness or physiologic stress, including surgery or
pregnancy, may precipitate or exacerbate the condition. The severity of the
condition varies from mild to severe, resulting in death. Neurologic
involvement includes bulbar palsy, loss of cranial and spinal motor nerve
function, wasting and fasciculation of the tongue, widespread muscle wasting
with weakness and hypotonia most obviously in neck and lower limb girdle.
Coordination and sensation remain intact. Respiratory complications include
nocturnal hypoventilation because of marked diaphragmatic weakness (forced
vital capacity [FVC] is severely reduced) and obstructive sleep apnea. Bulbar
nerve involvement causes laryngeal and pharyngeal dyscoordination, nasal
speech, and dysphagia with failure to protect the laryngeal inlet resulting
in aspiration episodes. Scoliosis and cervical subluxation have been
reported.
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Full neurologic assessment (degree
of bulbar involvement), chest radiography, respiratory function tests (in
advanced cases, the FVC is often reduced to <1 liter), arterial blood gas
analysis (hypercapnia). Consider postoperative need for mechanical
ventilation. Cervical spine radiograph may be indicated if any signs or a suspicion
for cervical subluxation exists.
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Bulbar nerve palsy may predispose to
aspiration in the perioperative period. There is a high risk of diminished
respiratory reserve and respiratory complications such as aspiration,
pneumonia, nocturnal hypoventilation, and hypercarbia. Bilateral deafness
may make communication during the perioperative period difficult. Regional
anesthesia may be appropriate (maintained consciousness, limited respiratory
depression, reduced risk of aspiration).
A rapid sequence induction technique is recommended, however keep in mind that
cervical subluxation requires special attention ...