Genetic disorder resulting in familial branchial
myoclonus, spastic paraparesis, and cerebellar ataxia.
Approximately 13 cases have been reported. The original description in 1988 reported
a family with six affected individuals in two generations. No other definite
case reports have been published.
The precise mechanism leading to this progressive
degenerative condition remains poorly understood. The levels of the
serotonin metabolite 5-hydroxyindoleacetic acid in the cerebrospinal fluid
(CSF) are low, and an abnormality in serotonin-mediated neurotransmission has been
proposed as a possible cause.
Made by clinical features consistent with the syndrome.
CT and MRI scans demonstrate severe atrophy of medulla, brainstem, and
cervical spinal cord, and mild atrophy of the cerebral and cerebellar
cortex, with normal pons and olives. CSF studies reveal a markedly reduced concentration
in the serotonin metabolite 5-hydroxyindoleacetic acid. Visual auditory and
somatosensory evoked responses, electroencephaloand electromyogram are normal.
Characterized by a rhythmic branchial myoclonus
(affecting palate, pharynx, larynx, lower face, and neck) resulting in dysphagia,
dysphonia, choking spells, spastic paraparesis (preserved, muscle strength
brisk reflexes, normal sensation), cerebellar ataxia (truncal), nystagmus,
and normal mental status. The age at onset usually is between 30 and 50 years.
The condition is progressive, leading to death or severe disability within 5
to 10 years of onset.
Detailed history and examination are
necessary to determine the progression of neurologic impairment (bulbar
palsy, degree of spastic paraparesis and cerebellar ataxia). Assess speech,
swallowing, and glottic competency (gastrostomy feeding, tracheostomy).
Pulmonary assessment (especially with a history of frequent aspiration episodes) by chest radiography,
spirometry, and arterial blood gas analysis. Evaluate motor impairment (wheelchair bound).
There is an increased risk of aspiration as a result
of laryngeal incompetence (consider awake fiberoptic or a rapid sequence
induction for tracheal intubation). Spastic paraparesis may lead to fixed
limb deformities with difficulty in positioning and venous access.
These patients have normal sensation in affected
limbs (and hence normal analgesic requirements). The potential risk for
postoperative ventilation, tracheostomy, and feeding gastrostomy should be considered.
Suxamethonium should be avoided
(hyperkalemia, rhabdomyolysis, arrhythmia, myoglobinuria, cardiac arrest).
Acid aspiration prophylaxis is recommended (H2 blockers, antacids).
Treatment with 5-hydroxytryptophan and carbidopa at highest tolerated doses
may improve ataxia, but not myoclonus.
De Yebenes JG, Vazquez A, Rabano J, et al: Hereditary branchial myoclonus
with spastic paraparesis and cerebellar ataxia: A new autosomal dominant
disorder. Neurology 38:569, 1988.
Howard RS, Greenwood R, Gawler J, et al: A familial disorder associated with
palatal myoclonus, other brainstem signs, tetraparesis, ataxia and Rosenthal
fiber formation. J Neurol Neurosurg Psychiatry