230 Journal ofNeurology, Neurosurgery, and Psychiatry 1991;54:230-235 Neuromyotonia in hereditary motor neuropathy J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.54.3.230 on 1 March 1991. Downloaded from A F Hahn, A W Parkes, C F Bolton, S A Stewart Abstract Case II2 Two siblings with a distal motor This 15 year old boy had always been clumsy. neuropathy experienced cramping and Since the age of 10, he had noticed generalised difficulty in relaxing their muscles after muscle stiffness which increased with physical voluntary contraction. Electromyogra- activity such as walking upstairs, running and phic recordings at rest revealed skating. For some time, he was aware of repetitive high voltage spontaneous elec- difficulty in releasing his grip and his fingers trical discharges that were accentuated tended to cramp on writing. He had noticed after voluntary contraction and during involuntary twitching of his fingers, forearm ischaemia. Regional neuromuscular muscles and thighs at rest and it was more blockage with curare indicated hyperex- pronounced after a forceful voluntary con- citability of peripheral nerve fibres and traction. Muscle cramping and spontaneous nerve block suggested that the ectopic muscle activity were particularly unpleasant activity originated in proximal segments when he re-entered the house in the winter, of the nerve. Symptoms were improved for example, after a game of hockey. Since the with diphenylhydantoin, carbamazepine age of twelve, he had noticed a tendency to and tocainide. trip. Subsequently he developed bilateral foot drop and weakness of his hands. He denied sensory symptoms and perspired only with The term "neuromyotonia" was coined by exertion. Mertens in 1965' to define a syndrome He was muscular with well-developed prox- of delayed muscle relaxation after voluntary imal muscles. This contrasted with moderate contraction resulting from a disorder of peri- wasting and weakness of the wrist and finger pheral nerve rather than muscle. Affected extensors, the intrinsic hand muscles and also patients complain of muscle stiffness and the peroneal and intrinsic fott muscles. Sen- cramping and show fasciculations and myo- sory examination was normal. Deep tendon kymia. Regional neuromuscular blockade with reflexes were reduced and ankle jerks were curare established the neural origin;'2 in fact, absent. The plantar responses were flexor. hyperexcitability and ectopic impulse genera- When he was fully relaxed, brief, repetitive tion may occur along the whole length of the twitching of his fingers and myokymia and motor axon, including the terminal arborisa- fasciculations in the proximal muscles were tions.3 Moreover, hyperexcitability of nerve clearly apparent. After forceful flexion of the http://jnnp.bmj.com/ membranes may be present in sensory, as well fingers, the grip release was slow and delayed, as motor axons, in spite of few sensory symp- with the appearance of action myotonia, yet toms.2 percussion of the thenar eminence produced Neuromyotonia has been observed with or no abnormal muscle contraction. Percussion without overt peripheral neuropathy.4 There of the tongue, however, resulted in a focal are, however, few descriptions of hereditary tonic contraction, lasting several seconds, neuropathies with associated neuro- which subsided into fasciculations. Strong on October 1, 2021 by guest. Protected copyright. myotonia,259 and the precise mechanisms of voluntary contraction of his quadriceps was the neuromyotonia are still in some doubt. followed for 10 to 30 seconds by a persisting, Department of We Clinical Neurological report our observations in two siblings involuntary contraction of the muscles, which Sciences, University of of Chinese origin, born to unrelated, healthy subsided into myokymic activity and fas- Western Ontario, parents. Symptoms of neuromyotonia had ciculations. The Trousseau sign was positive. London and the been present since Victoria Hospital, early childhood, accom- Within 10 seconds after inflation of a blood London, Ontario panied by a progressive motor deficit in distal pressure cuff, the fingers began to twitch and A F Hahn muscles of the upper and lower limbs. Elec- by 35 seconds they were drawn into a carpal A W Parkes trophysiological studies provided further C F Bolton clues on the mechanisms of the abnormal St Joseph's Hospital, 1 2 London, Ontario, spontaneous nerve activity. A favourable Canada therapeutic response was seen with diphenyl- I S A Stewart hydantoin, carbamazepine and tocainide. Correspondence to: Dr Hahn, Department of Clinical Neurological Sciences, Victoria Hospital, Case reports 375 South Street, London, The family tree is illustrated in fig 1. All Ontario N6A 4G5, Canada family members received a full clinical and Received 2 April 1990 and in Figure 1 Family tree, only II2 and II5 were affected. revised form 13 July 1990. electrophysiological examination. Only II2 Detailed electrophysiological testing and biopsies were Accepted 23 July 1990 and II5 were affected. performed in I2. Neuromyotonia in hereditary motor neuropathy 231 spasm, which resolved quickly when the cuff Regional neuromuscular blockade: an intraven- J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.54.3.230 on 1 March 1991. Downloaded from was deflated. ous regional infusion of delta-tubocurare was Treatment with carbamazepine, 400 mg/ given to patient II2 in the right forearm. This day resulted in a marked improvement of the was erformed after informed consent with neuromyotonic symptoms in that he could proper precautions according to the methods of release his grip promptly, movements were Torda and Klonymus.' A total of 17 ml of a smooth and he could run up two flights of 0-028% solution of delta-tubocurare was injec- stairs with only mild muscle stiffening. ted over a period of 21 minutes. This resulted Tongue myotonia was no longer present. in the gradual disappearance of all abnormal Unfortunately, carbamazepine had to be spontaneous activity. discontinued after two weeks because of Ulnar nerve block: 7 ml of 2% xylocaine were thrombocytopenia. Diphenylhydantoin, injected near the ulnar nerve at the elbow. 300 mg/day was less effective. While there was Assessment ofthe block was made by recording little spontaneous muscle activity at rest, it the maximum hypothenar muscle compound was readily recorded with surface and action potential in response to supramaximal needle electrodes after voluntary contraction stimulation of the ulnar nerve at the wrist, and during ischaemia. Tocainide, 1200 mg/ below the elbow and above the elbow, before, day resulted in excellent symptomatic during and after the xylocaine injection. improvement of the delayed muscle relaxation Polygraph recordings of spontaneous activity and generalised muscle stiffness. Yet involun- from both hypothenar muscles were made with tary, brief muscle twitching persisted, surface electrodes before, during and after provoked by muscle activation and nerve recovery of the xylocaine block. ischaemia. The favourable therapeutic Polygraph recordings: simultaneous recordings response has been maintained, but muscle were made with surface electrodes from all four cramping recurred promptly when the drug limbs, while monitoring EKG and respiration. was discontinued. Muscle Biopsy: cryostat sections of the anterior tibial muscle were stained or reacted for Case 115 haematoxylin and eosin, Gomori trichrome, Symptoms were much milder in his younger DPNH and ATPase. A piece of muscle was sister who was examined at the age of 11. She fixed in 2-5% buffered glutaraldehyde and denied any limitations. Examination showed processed for electron microscopy according to no spontaneous involuntary muscle activity at standard techniques. One micron toluidine rest. Muscle tone was normal. Selective weak- blue-stained sections were examined with the ness was demonstrable in wrist and finger light microscope; ultrathin sections of selected extensors and peroneal muscles. Definite per- areas were viewed with an electron microscope cussion myotonia was present in the tongue (Philips 410). but none in the thenar eminence. Grip release was not delayed. Deep tendon reflexes and the sensory examination were normal. In spite of Results only mild clinical findings, bursts of high vol- Laboratory examinations were normal, includ- tage, spontaneous electrical activity were ing serum sodium, potassium, chloride, cal- recorded in many proximal and distal limb bicarbonate, inorganic cium, magnesium, http://jnnp.bmj.com/ muscles at rest and accentuated after activity. phosphate, creatinine and thyroid indices. Creatinine phosphokinase was elevated in II2 to Material and methods 1248 U/L (36-188). It was normal in all other Electrophysiology family members. Standard nerve conduction studies were per- Electrophysiology: nerve conduction studies in formed-orthodromic for motor and II2 and II5 revealed entirely normal motor and antidromic for sensory, utilising surface elec- sensory conduction velocities, however, com- trodes. Needle electromyography was carried pound muscle action potentials were reduced on October 1, 2021 by guest. Protected copyright. out with a concentric needle electrode. in amplitude and distal latencies were con- Polygraph recordings were made with a Model siderably prolonged (table). F-wave latencies 8-16 Grass EEG machine while respiration could not be measured, due to the persistent was recorded with a Phipps and Bird neuromyotonia. Needle electromyography of pneumograph. distal