Robert B. Layzer

Dihydropyridine Receptor Mutations Cause Hypokalemic Periodic Paralysis

Hypokalemic periodic paralysis (hypoKPP) is an autosomal dominant skeletal muscle disorder manifested by episodic weakness associated with low serum potassium. Genetic linkage analysis has localized the hypoKPP gene to chromosome 1q31-q32 near a dihydropyridine (DHP) receptor gene. This receptor functions as a voltage-gated calcium channel and is also critical for excitation-contraction coupling in a voltage-sensitive and calcium-independent manner. We have characterized patient-specific DHP receptor mutations in 11 probands of 33 independent hypoKPP kindreds that occur at one of two adjacent nucleotides within the same codon and predict substitution of a highly conserved arginine in the S4 segment of domain 4 with either histidine or glycine. In one kindred, the mutation arose de novo. Taken together, these data establish this DHP receptor as the hypoKPP gene. We are unaware of any other human diseases presently known to result from DHP receptor mutations.

MRI findings in Susac’s syndrome

Background: Susac syndrome (SS) is a self-limited syndrome, presumably autoimmune, consisting of a clinical triad of encephalopathy, branch retinal artery occlusions, and hearing loss. All three elements of the triad may not be present or recognized, and MR imaging is often necessary to establish the diagnosis. Objective: To determine the spectrum of abnormalities on MRI in SS. Methods: The authors reviewed the MR images of 27 previously unreported patients with the clinical SS triad, and 51 patients from published articles in which the MR images were depicted or reported. Results: All 27 patients had multifocal supratentorial white matter lesions including the corpus callosum. The deep gray nuclei (basal ganglia and thalamus) were involved in 19 (70%). Nineteen (70%) also had parenchymal enhancement and 9 (33%) had leptomeningeal enhancement. Of the 51 cases from the literature, at least 32 had callosal lesions. The authors could not determine the presence of callosal lesions in 18 of these patients, and only one was reported to have a normal MRI at the onset of encephalopathy. Conclusions: The MR scans in SS show a rather distinctive pattern of supratentorial white matter lesions that always involve the corpus callosum. There is often deep gray matter, posterior fossa involvement, and frequent parenchymal with occasional leptomeningeal enhancement. The central callosal lesions differ from those in demyelinating disease, and should support the diagnosis of SS in patients with at least two of the three features of the clinical triad.

Neuropathy following abuse of nitrous oxide

A disabling peripheral neuropathy, mainly sensory, developed in three health workers who habitually abused nitrous oxide. The distinctive clinical picture included patterns of numbness that were radicular rather than purely distal, and a “reverse” Lhermitte sign, in the absence of signs of spinal cord involvement. Nerve conduction studies suggested an axonal rather than demyelinative neuropathy. The neurologic disorder improved slowly when the patients abstained from further nitrous oxide abuse.

Wolfram syndrome Evidence of a diffuse neurodegenerative disease by magnetic resonance imaging

Wolfram syndrome is an autosomal recessive disorder beginning in childhood that consists of four cardinal features: optic atrophy, diabetes mellitus, diabetes insipidus, and neurosensory hearing loss. Aside from these features, the clinical picture is highly variable and may include other neurologic abnormalities such as ataxia, nystagmus, mental retardation, and seizures. We present two unrelated patients with Wolfram syndrome, both of whom had the four cardinal features and several other neurologic abnormalities. MRIs showed widespread atrophie changes throughout the brain, some of which correlated with the major neurologic features of the syndrome.

The declining electrical response of muscle to repetitive nerve stimulation in myotonia

The electrical response of muscle to repetitive nerve stimulation was studied in patients with various myotonic disorders. A decrementing response was a common but not invariable finding, and was unrelated to the severity or diagnosis. The decrement either continued throughout the period of stimulation or “leveled off,” sometimes being followed by an increment. If it occurred at low rates of stimulation, a greater decrement occurred at higher rates, usually after a shorter latent period. It was not related consistently to the presence of weakness, but in patients with myotonia congenita it was more conspicuous and elicited by lower rates of stimulation when transient weakness was a feature of the history.

Adult-onset nemaline myopathy: Another cause of dropped head.

A 59‐year‐old man with severe neck extensor weakness had findings diagnostic of nemaline myopathy on muscle biopsy. Review of the literature shows that dropped head occurs in nearly half of the patients with adult‐onset nemaline myopathy. Other leading causes of dropped head syndrome are amyotrophic lateral sclerosis, myasthenia gravis, and isolated neck extensor myopathy.

Emery-Dreifuss muscular dystrophy with autosomal dominant transmission.

A woman with early-onset, slowly progressive, humeroperoneal muscle weakness had marked restriction of neck flexion with contracture at the elbows. She developed exertional dyspnea at age 25, atrial fibrillation with slow ventricular rate was discovered, and a cardiac pacemaker was implanted. Her father had a similar disorder. There is at least one other report of autosomal dominant transmission of this clinical picture, which had previously only been reported as Emery-Dreifuss muscular dystrophy with X-linked recessive inheritance. Thus, more than one mode of inheritance is possible for this unusual and distinctive form of muscular dystrophy.

Continuous cataplexy in a patient with a midbrain tumor The limp man syndrome

A patient with glioblastoma of the rostral brainstem and hypothalamus exhibited bilateral internuclear ophthalmoplegia and vertical nystagmus; he suffered episodes of cataplexy, narcolepsy, and sleep paralysis. A peculiar fluctuation of posture and tone (“limp man syndrome”) proved to be a manifestation of continuous cataplexy, as documented by H-reflex recordings. This is the first report of a remarkable movement disorder caused by continuous, fluctuating, partial cataplexy, and is the second report of an association between cataplexy and a tumor of the rostral brainstem.

Neurologic complications of lumbar epidural anesthesia and analgesia

We reviewed the clinical features of 12 patients with neurologic complications following lumbar epidural anesthesia or analgesia.Eleven patients experienced lumbosacral radiculopathy or polyradiculopathy and, of these, 10 received epidural anesthesia or analgesia and one received subarachnoid injection of medication after intended epidural anesthesia. One patient suffered a moderately severe thoracic myelopathy in the setting of unintended spinal anesthesia. The two patients with more severe polyradiculopathy had severe lumbar spinal stenosis on MRI. The other patients experienced mild to moderate neurologic deficits most often involving the L-2 root, and MRIs, when performed, were unremarkable. EMG on three patients helped to localize the lesions to the lumbosacral roots and to quantify the extent of axonal loss. Ten patients were ambulatory upon discharge from the hospital and had good neurologic outcome. One patient with severe polyradiculopathy did not improve after 4 years and had severe motor axonal loss based upon electrodiagnostic studies. The patient with a thoracic myelopathy was ambulatory 4 months after onset. Although generally a safe procedure with low frequency of complications, lumbar epidural anesthesia or analgesia occasionally causes neurologic sequelae such as radiculopathy or myelopathy. Neurologic complications may be more severe in the presence of spinal stenosis or after inadvertent subarachnoid injection of anesthetic or analgesic agent. NEUROLOGY 1995;45: 1795-1801

Partial deficiency of cardtine palmityltransferase Physiologic and biochemical consequences

Deficiency of muscle carnitine palmityltransferase (CPT), first described in 1973 by DiMauro and associates, is proving to be one of the principal causes of recurrent paroxysmal myoglobinuria. In this disease, oxidation of lipid substrates is impaired, because CPT is necessary for the transport of long-chain fatty acids through the inner mitochondrial membrane. As a result, patients depend excessively on carbohydrate metabolism as a source of energy for muscular work.Deficiency of muscle carnitine palmityltransferase (CPT), first described in 1973 by DiMauro and associates,l,2 is proving to be one of the principal causes of recurrent paroxysmal myoglobinuria. In this disease, oxidation of lipid substrates is impaired, because CPT is necessary for the transport of long-chain fatty acids through the inner mitochondrial membrane. As a result, patients depend excessively on carbohydrate metabolism as a source of energy for muscular work.