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Biopsy specimens of skeletal muscle from a family that had three female siblings with clinical features of recessive-type myotonia congenita were examined by light and electron microscopy. Fibers examined by the former technique appeared normal. Although some variation in size and shape of mitochondria and sarcomere fragmentation were focally observed by electron microscopy in affected members, they were also encounted in those without clinical manifestations. Importantly, no changes in sarcolemma, sarcoplasmic reticulum, or transverse tubular system were encountered. Capillary basement membrane thickness was within normal limits. The evidence strongly suggests that myotonia congenita represents an entity distinct from myotonia dystrophica and that its pathogenesis may be related to a biochemical rather than ultrastructal aberration.

The report deals with the results of a clinico-morphological study of 14 patients with Thomsen's myotonia. The muscles obtained during biopsy were studied by electron microscopy. It was established that in patients with a mild and moderate degree of the disease the muscle fibres did not differ from normal ones. Only in patients with severe forms of the disease was it possible to detect focal changes of the myofebrillar apparatus, a moderate hypertrophy of the sacrotubular system and an enlargement in the size of the mitochondria. These changes as it is assumed, are morphological expression of the myotonic phenomenon and reflect the changed functional relationships in the link Ca-troponin-actomyosine complex.

A 35 years old man has a non progressive muscle disease which appeared when he was 6. Clinically, there is a slight muscle hypertrophy, an important spontaneous myotonia and a curious muscle weakness, quite marked on the first efforts, but disappearing entirely after a few muscle contractions. The E.M.G. is normal but for the myotonic reaction. Muscle biopsy shows a selective atrophy of type II fibers. The disease is a genetic one, a sister and a brother of our patient having noticed the same symptom. The place of this disease among the congenital myotonias is discussed.

We have investigated the muscle biopsies of 8 patients with myotonia congenita. There were 2 families with autosomal recessive inheritance (5 cases), 1 with autosomal dominant inheritance, and 2 sporadic cases. Mild abnormalities were seen with routine pathological preparations which were nondiagnostic. Histochemical studies of fiber subtypes demonstrated a complete absence of Type 2B muscle fibers in all of our patients regardless of the type of inheritance. this is the first reporot of an entity in which there is a consistent absence of a muscle fiber type, and some speculation has been made as to the possible causes.

In 12 patients with paramyotonia congenita, percutaneous needle biopsies from the brachial biceps muscle were performed. Muscle fibre area, distribution of muscle fibre types I, II-A and II-B and capillarization were not different from healthy controls. Signs of myopathy with central nuclei in the muscle cells were noted in 9 of the patients. 4 of these patients also had small areas with degeneration and, in one, vacuoles were observed. Quantitative determination of muscle glycogen, water and protein content were within normal range as were enzyme activities for hexokinase, lactate dehydrogenase, citrate synthetase and 3-hydroxy-acyl-CoA dehydrogenase.

Myotonia congenita was diagnosed in a 12-week-old female Chow Chow that had hindlimb ataxia, a stiff gait, and occasional collapsing. The diagnosis was based on the history, clinical signs, electrodiagnostics, and microscopic examination of biopsied muscle specimens.

We report 3 patients with a myopathy characterized by profound selective muscle wasting and weakness, electrical myotonia without clinical myotonia and an unusual muscle biopsy. Cryostat sections showed muscle fibers with vacuoles containing hematoxylinophilic granules, and 30% of type I fibers showed demarcation of their sarcoplasm into "lobules" due apparently to reorganization of myofibrillar elements. The electrical myotonia suggests an underlying muscle membrane defect. Two of the patients are siblings suggesting that the disorder may be inherited.

The regenerative ability of muscles was studied in various neuromuscular disorders by quantitative electron microscopy using two indices of both the satellite cell population and the euchromatin percentage of satellite cell nucleus. Both the number of satellite cells and the euchromatin percentage were increased in polymyositis. Duchenne muscular dystrophy and myotonic dystrophy showed only an increased number of satellite cells without increased euchromatin percentage, while amyotrophic lateral sclerosis had only an increased euchromatin percentage without increased satellite cell number. These results suggest that some defects of satellite cell function probably exist in progressive muscular dystrophy and amyotrophic lateral sclerosis, while in polymyositis the muscle fiber may have the ability to regenerate completely. The euchromatin percentages of myonuclei were increased in polymyositis and Duchenne muscular dystrophy, but not in amyotrophic lateral sclerosis or myotonic dystrophy compared to those of controls. This suggests the activated function of the remaining muscle fibers in polymyositis and Duchenne muscular dystrophy.

The nosographic relationship between Thomsen's and Steinert's disease is still uncertain. There is not agreement in the literature whether these are two different diseases or just different stages in the evolution of a single one. Four members of a family in two generations have been studied: two have a typical Steinert's, one a Thomsen's disease and one a clinical pattern that cannot be clearly considered neither of the first nor of the second type. In this patient a generalized muscular hypertrophy was followed, at the age of 54, by a generalized impairment of the muscular trophism and evolved into a severe wasting. This may be interpreted as an evolution of Thomsen's into a Steinert's disease. Furthermore, the presence in the same family of cases of both Thomsen's and Steinert's disease supports the hypothesis of a single disease. The present study suggests that Thomsen's and Steinert's diseases could be two clinical varieties of a single disease in different stages of development. This conclusion is supported by the similarity in the electromyographic patterns and in the histological picture from muscle biopsy of all patients examined.

We reported a case of Becker type congenital myotonia with myalgia. A 28 year-old woman admitted to our hospital because of right anterior chest pain and back pain. She was diagnosed as myotonic dystrophy by other university hospital when she was 16 years old. Physical examination revealed only myotonia and could not find muscle atrophy or cataracta which were usually found in myotonic dystrophy. The quadriceps muscle biopsy revealed complete absence of type IIB muscle fiber. We diagnosed her Becker type congenital myotonia by the clinical course and family history and the histopathological findings of quadriceps muscle. Myalgia which she complained seemed to have some connection with this disease. But we could not prove the pathogenesis of this myalgia.

We report a family in which two sisters with myotonia congenita (MyC) were referred for malignant hyperthermia (MH) evaluation after each developed muscle rigidity with anesthesia. Halothane contracture testing of skeletal muscle in both was consistent with MH susceptibility. A third sister without clinical evidence of MyC was negative on contracture testing. These results suggest an association between MyC and MH susceptibility.

Recommendations for histological criteria of diagnosis of dystrophic and congenital myotony as well as familial hypopotassemic periodic paralysis based on the results of skeletal muscles biopsies are presented.

The authors have reported the results of examination by electron microscopy of two muscle biopsy specimens from cases of myotonia congenita and three cases of myotonia dystrophica. They have stated that "peripheral annular formation" was a frequently observed alteration in the myotonia congenita cases. In the myotonia dystrophica cases there were additionally disorganized myofibrils in the subsarcolemmal region and inclusion body vacuoles morphologically connected with the sarcolemma. The term "peripheral annular formation" refers to the situation in which the peripheral myofibrils of the muscle fiber fracture and the fragments retract and form a helical sheath around the central myofibrils of the same muscle fiber.

Acetazolamide has been shown to be effective prophylaxis for both hypokalemic and hyperkalemic paralysis. A patient with paramyotonia congenita, a related disorder with myotonia and episodic weakness, was studied during treatment with acetazolamide. Athough the patient's myotonia was virtually abolished, severe quadriparesis was produced during each trial of acetazolamide. This response distinguished this patient's condition from other forms of familial periodic paralysis and suggests that acetazolamide may be deleterious to some patients with periodic paralysis.

We have studied 14 patients from a kindred with an autosomal dominant form of myotonia, with features differing from most cases of autosomal dominant or recessive myotonia congenita. All patients had painful muscle stiffness that was provoked by fasting and oral potassium administration and was relieved by carbohydrate-containing foods. Muscle biopsies showed the presence of type 1, 2A, and 2B fibers, as opposed to the absence of type 2B fibers seen in some patients with myotonia congenita. Acetazolamide was dramatically effective in alleviating myotonia in all patients and was more effective than other antimyotonic agents.

A mutant mouse with a hereditary myotonia, 'arrested development of righting response', ADR, was investigated with respect to mononucleated cell populations in skeletal muscle. Upon enzymatic dissociation of different muscles from mice aged between 15 and 120 days, a 3- to 5-fold higher yield of mononucleated cells per muscle fresh weight was obtained from mice with the ADR syndrome than from control mice. Clonal cell culture showed that the absolute number of cells with myogenic potential was increased and that mutant clones had shorter generation times than wild-type controls. Morphological differentiation of ADR myotubes was indistinguishable from that of the controls. Light microscopy confirmed the presence of increased numbers of mononucleated cells per muscle volume. At the ultrastructural level, there were 3.3 times as many satellite cells (the myogenic stem cells of mature muscle) per myofibre nucleus in ADR than in controls. Because no fibre degeneration was observed in the ADR mutant, we conclude that the enlarged mutant satellite cell pool is not a result of compensatory proliferation but is a consequence of fibre-type transformation and/or delayed maturation of the myotonic muscle.

The histochemical ATPase fibre type pattern was examined in muscle biopsy samples obtained from patients with recessive myotonia, paramyotonia and from one patient with dominant myotonia. Absence (less than or equal to 5%) of 2B fibres was a genuine finding in the minority of the cases. In additional cases of recessive myotonia, a deficiency (less than or equal to 15%) of 2B fibres was observed. Absence or deficiency of 2B fibres was not related to the minor myopathic alterations or to (para-)myotonic activity. It is hypothesised that absence of 2B fibres is a dominant or a recessive autosomal trait, and deficiency of 2B fibres is a recessive trait. Reported findings and our own observations suggest the possibility of a genetic combination of myotonia and absence/deficiency of 2B fibres. Implications of these hypotheses are proposed.

In isolated fiber bundles of external intercostal muscle from each of 13 normal volunteers and each of 6 patients with myotonia congenita, some or all of the following were measured: concentrations of Na(+), K(+), and Cl(-), extracellular volume, water content, K(+) efflux, fiber size, fiber cable parameters, and fiber resting potentials. Muscle from patients with myotonia congenita differed significantly (0.001