Muscle & nerve
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Neuromuscular hyperexcitability is a characteristic of Isaacs' syndrome. Autoantibodies specific for voltage-gated potassium channels (VGKC) or ganglionic nicotinic acetylcholine receptors (AChR) are markers of this disorder. To determine the frequency of these ion channel antibodies and of related neuron- and muscle-specific antibodies in patients with acquired neuromuscular hyperexcitability, we tested serum specimens from 77 affected patients (35 neuromyotonia, 32 cramp-fasciculation syndrome, 5 rippling muscle syndrome, and 5 focal neuromuscular hyperexcitability) and 85 control subjects. ⋯ Overall, 55% had serological evidence of neurological autoimmunity compared to 2% of control subjects. Patients with neuromyotonia were more frequently seropositive (71%) than patients with cramp-fasciculation syndrome (31%). We conclude that acquired neuromuscular hyperexcitability consists of a continuum of clinical disorders with a common autoimmune pathogenesis.
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Fabry's disease is commonly associated with a painful, debilitating neuropathy. Characterization of the physiological abnormalities is an important step in evaluating response to specific therapies. Twenty-two patients with Fabry's disease, and with relatively preserved renal function, underwent conventional and near-nerve conduction studies, electromyography, sympathetic skin responses, and quantitative sensory testing (QST). ⋯ Cold thresholds were more often abnormal than were warm thresholds. Vibration thresholds were normal in the feet and, in some patients, elevated in the hand only, probably due to frequent median nerve entrapment at the wrist. Our findings suggest that the neuropathy of Fabry's disease is characterized by an increased prevalence of median nerve entrapment at the wrist and by thermal afferent fiber dysfunction in a length-dependent fashion, with greater impairment of cold than warm sensation.
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Case Reports
Anomalous superficial radial nerve: a patient with probable autosomal dominant inheritance of the anomaly.
The sensory symptoms due to lesions of the superficial branch of the radial nerve are usually limited to the dorsolateral area of the hand. We describe a 40-year-old woman who presented with numbness of the dorsomedial aspect of the right hand following arthroplasty of the wrist. Clinically, the sensory loss suggested a lesion of the dorsal branch of the ulnar nerve. ⋯ Antidromic stimulation of the dorsal branch of the ulnar nerve and superficial branch of the radial nerve with paired surface recording of sensory nerve action potentials from the dorsolateral (radial side) and dorsomedial (ulnar side) hand is useful for evaluating this anomaly. Our patient had two children, one of them with a similar anomaly. This suggests an autosomal dominant inheritance of the anomaly.
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Intramuscular injection of botulinum toxin A is used to treat focal dystonias. Because immunoresistance has been documented in some patients, other molecular forms of the toxin have been evaluated clinically. The present investigation compared the time course and extent of neuromuscular blockade and recovery of botulinum toxin types A and F using an electromyographic monitoring system implanted in the rat hindlimb. ⋯ Conversely, animals receiving type F toxin fully recovered within 30 days at all dose levels. The rapid recovery with type F toxin suggested that neuromuscular transmission was restored via the original terminals rather than through functional collateral sprouting. The reversible nature of blockade with this molecular species puts in question its future clinical utility.