Dantrolene sodium does influence the second-wind phenomenon in McArdle's disease. Electrophysiological evidence during exercise in a double-blind placebo-controlled, cross-over study in 5 patients.

Five patients with McArdle's disease entered a double-blind, placebo-controlled, cross-over study of dantrolene sodium. None of the patients experienced beneficial effect of dantrolene sodium medication. Each patient performed 2 exercise tests. Surface EMG during exercise tests without medication showed a temporary increase in EMG activity during the adaptation phase. Quite unexpectedly however, in view of the negative clinical results, this electrophysiological manifestation of muscle fatigue during the adaptation phase diminished or disappeared in all patients investigated when dantrolene sodium was used.

Dihydropyrimidine dehydrogenase deficiency. Neurological aspects.

A family with dihydropyrimidine dehydrogenase (DPD) deficiency is presented. In 3 persons a complete deficiency, and in 3 others a partial deficiency was detected in cultured fibroblasts. Two homozygote subjects and 1 heterozygote subject suffered from epileptic manifestations, in one of these homozygote subjects also microcephaly was found. DPD deficiency might be an etiological factor in the clinical picture of these patients. An autosomal recessive mode of inheritance of this deficiency was found.

Cranio-vertebral pathology in Down syndrome.

Cranio-vertebral malformations, especially atlanto-axial dislocation, are frequently seen in Down patients. However, symptomatic forms in mongolism are rare. Pyramidal signs have a signal value. In symptomatic malformations surgical treatment should be advised, i.e. posterior fixation after pre-operative reduction by traction or transoral odontoidectomy if no reduction is achieved.

Increase in median power frequency of the myoelectric signal in pathological fatigue.

During bicycle ergometry, surface EMG analysis was performed on the m. vastus lateralis in a patient with pathological fatigue (due to skeletal muscle carnitine deficiency). With prolonged, submaximal, exercise (30% VO2 max, 2 h) the median frequency of the power density spectrum increased, despite fatigue and lactate production. This observation questions the general validity of the present concepts on myoelectric aspects of fatigue.

Exertional rhabdomyolysis in a patient with calcium adenosine triphosphatase deficiency.

A patient with exertional rhabdomyolysis and continuously elevated serum creatine kinase (CK) was investigated. The known causes of recurrent attacks of rhabdomyolysis were ruled out by appropriate histochemical and biochemical investigations. During ischaemic exercise tests an abnormal K(+)-efflux from exercising muscles was observed. The patient was found to have a deficiency of muscular Ca(2+)-ATPase. Dantrolene sodium therapy gave relief of muscle symptoms and improved the exercise tolerance. Both the CK level and the K(+)-efflux in ischaemic forearm testing became normal on this therapy.

The second wind phenomenon in McArdle's disease.

Three patients with McArdle's disease exercised for 2 h at 30% VO2max. During exercise two phases occurred. During the first 15 min they experienced progressive fatigue and weakness of exercised muscles, with a rapid and complete recovery (adaptation phase). Following this, all 3 patients were able to continue exercise without difficulty ('second wind' phase). During the adaptation phase, patients have to cope with their inability to use muscle glycogen as a fuel. Processes occurring during this phase are as follows. An increase in cardiac output. This might be expected to increase muscle blood flow in order to supply exercising muscle with substrates that can substitute for muscle glycogen (free fatty acids (FFA), bloodborne glucose). Changes in the metabolic pathways. These cause a sufficient amount of hexose phosphates to be present to overcome the first 2.5 min of exercise, and FFA and bloodborne glucose to play a major role in energy supply at an earlier stage in exercise than in control subjects. An increase in EMG activity. This is most probably caused by the recruitment of more motor units to compensate for a failure of force generation in the muscle fibres. Central command seems to play an important role in the regulation of cardiovascular processes during the adaptation phase. Despite these compensatory mechanisms, metabolic stress occurs during the adaptation phase. During the 'second wind' phase there are no important differences between the metabolism of exercising muscle of patients with McArdle's disease and that of control subjects.