Proximal myotonic myopathy

Three Swedish patients with proximal muscle weakness, myotonia and lack of CTG expansion on genetical analysis are presented. Clinical neurological and neurophysiological examination and muscle biopsy were performed. There was an indication of autosomal dominant inheritance in 2 of the 3 patients. The main symptoms and clinical findings in the 3 patients were weakness of the proximal muscles, myotonia, muscle stiffness, muscle pain and muscle atrophy. Neurophysiological examination showed myotonic bursts and muscle biopsy snowed a variation of fibre sizes, an increased number of muscle fibres with centralized nuclei and scattered atrophic muscle fibres. Laboratory data showed elevated CK, GT and LD in 1 patient. Before genetical analysis was performed, all 3 patients had been diagnosed as atypical cases of myotonic dystrophy. However, the symptoms, clinical signs, laboratory data, electrophysiological and muscle biopsy findings were compatible with proximal myotonic myopathy (PROMM).     

Altered gating and conductance of Na+ channels in hyperkalemic periodic paralysis

Electrophysiological studies on muscle fibres from patients with hyperkalemic periodic paralysis with myotonia have shown that the episodes of weakness are caused by a sustained depolarization of the sarcolemma to potentials between -40 and -60 mV. In muscle fibre segments from three such patients this sustained depolarization was caused by noninactivating Na⁺ channels with reduced single-channel conductance blocked by TTX and procainamide. As the chloride conductance was normal, myotonia may be best explained with the abnormal reopenings of the Na⁺ channels. The recently described genetic linkage between hyperkalemic periodic paralysis with myotonia and the gene coding for the TTX-sensitive Na⁺ channel suggests an altered primary structure of this channel causing its abnormal function.     

Novel chloride channel gene mutations in two unrelated Japanese families with Becker's autosomal recessive generalized myotonia

We investigated the skeletal muscle voltage-gated chloride channel gene (CLCN1) in two unrelated Japanese patients with Becker's myotonia congenita. The non-myotonic parents of each patient were consanguineous. The proband of each family shares generalized myotonia, transient weakness after rest, and leg muscle hypertrophy. However, the disease severity related to the degree of myotonia differed, even in view of the response to long train nerve stimulation tests. CLCN1 gene analysis revealed a novel Ala659Val missense mutation identified to be homozygous in the more severe patient, while a novel Gln445Stop nonsense mutation was present in the other patient. Both mutations were absent in 90 Japanese normal controls. This is the first report of Japanese cases of Becker's myotonia congenita with CLCN1 gene mutations.     

口服左氧氟沙星片致帕金森综合征1例

左氧氟沙星 (ｌｅｖｏｆｌｏｘａｃｉｎ)是第 3代喹诺酮类抗菌药物 ,其抗菌谱广 ,对革兰阳性及革兰阴性细菌均有较好抗菌作用[1 4 ] 。其不良反应有恶心、呕吐、上腹不适、腹痛、腹泻等 ,变态反应 ,还有头晕[2 ] 、兴奋、失眠[3 ] 、味觉异常等[5] 。笔者未见引起帕金森综合征的报道 ,现遇见 1例报道如下病人 ,男 ,60ａ ,因“慢性支气管炎急性发作” ,医生予左氧氟沙星片 (商品名 :京必妥新 ,浙江新昌京新制药有限公司生产 ,批准文号 :国药准字Ｘ19990 0 60 ,每片 0 .1ｇ) 0 .2ｇ ,每日 2次及常规用量的溴己新 (ｂｒｏｍｈｅｘｉｎ)口服治疗…     

Guidelines on clinical presentation and management of nondystrophic myotonias

The nondystrophic myotonias are rare muscle hyperexcitability disorders caused by gain-of-function mutations in the SCN4A gene or loss-of-function mutations in the CLCN1 gene. Clinically, they are characterized by myotonia, defined as delayed muscle relaxation after voluntary contraction, which leads to symptoms of muscle stiffness, pain, fatigue, and weakness. Diagnosis is based on history and examination findings, the presence of electrical myotonia on electromyography, and genetic confirmation. In the absence of genetic confirmation, the diagnosis is supported by detailed electrophysiological testing, exclusion of other related disorders, and analysis of a variant of uncertain significance if present. Symptomatic treatment with a sodium channel blocker, such as mexiletine, is usually the first step in management, as well as educating patients about potential anesthetic complications.     

Autosomal Recessive Axonal Neuropathy With Neuromyotonia: A Rare Entity

BackgroundAutosomal recessive axonal neuropathy with neuromyotonia is a recently described entity associated to the HINT1 gene, encoding histidine triad nucleotide-binding protein 1.PatientThe authors report a Portuguese 16-year-old girl of Roma ethnicity, descendant of consanguineous parents, with progressive distal muscular atrophy and weakness, beginning at age 6. After several years of extensive investigation with inconclusive results, clinical myotonia was identified. Electrophysiologic studies revealed neuromyotonia associated with a severe chronic predominantly motor axonal neuropathy and homozygous mutation (c.334 C > A, p.H112 N) in HINT1 was detected.ConclusionThis report emphasizes the late onset of clinical myotonia essential to the diagnosis.     

Histamine Formation and Catabolism in the Faeces with Special Reference to Dystrophia Myotonica

Faeces from patients with dystrophia myotonica and controls were incubated aerobically for 20-24 hours with L-histidine, L-carnosine, histamine diphosphate, N-acetylhistamine, and N-acetyl-L-histidine.

Whereas inherent histamine-like activity is stable in faeces from patients with dystrophia myotonica, histamine added to faeces with inherent histamine-like activity is degraded, although to a lesser degree than histamine added to patient faeces with low inherent histamine-like activity or to control faeces.

N-acetylhistamine is degraded in both control and patient faeces and a bioactive substance appears that seems to be identical with free histamine. N-acetyl-L-histidine also seems to be catabolized to free histamine in patient faeces.

In patient faeces with high inherent histamine-like activity, L-histidine is converted to histamine to a greater proportion than to urocanic acid and dihydrourocanic acid. The latter metabolites are prominent in control faeces, whereas only minute amounts of histamine are formed. On prolonged incubation, however, ample amounts of histamine are formed, and then the stability of Chistamine added to control faeces seems to increase. L-carnosine is also converted to a biologically active substance.

In dystrophia myotonica increased formation seems to be the main cause of the high inherent faecal histamine-like activity.     

The Overlap between Fibromyalgia Syndrome and Myotonia Congenita

BackgroundFibromyalgia syndrome (FMS) is a complex disorder characterized by chronic widespread pain (CWP), multiple areas of tenderness, sleep disturbance, fatigue, and mood or cognitive dysfunction. Myotonia congenita (MC) is an inherited myopathic disorder that is caused by mutations in the gene encoding the skeletal muscle chloride channel, which can infrequently manifest as generalized muscle cramps or myalgia.ConclusionsThese two cases are the first report of an overlap of CWP between FMS and MC.     

Muscle phenotype in patients with myotonic dystrophy type 1

Introduction: The pathogenesis of muscle involvement in patients with myotonic dystrophy type 1 (DM1) is not well understood. In this study, we characterized the muscle phenotype in patients with confirmed DM1. Methods: In 38 patients, muscle strength was tested by hand‐held dynamometry. Myotonia was evaluated by a handgrip test and by analyzing the decrement of the compound muscle action potential. Muscle biopsies were assessed for morphological changes and Na⁺‐K⁺ pump content. Results: Muscle strength correlated with a decline in Na⁺‐K⁺ pump content (r = 0.60, P < 0.001) and with CTG expansion. CTG expansion did not correlate with severity of myotonia, proximal histopathological changes, or Na⁺‐K⁺ pump content. Histopathologically, we found few centrally placed nuclei (range 0.2–6.9%). Conclusions: The main findings of this study are that muscle weakness correlated inversely with CTG expansion and that central nuclei are not a prominent feature of proximal muscles in DM1. Muscle Nerve 47:409‐415, 2013