A retrospective study of accuracy and usefulness of electrophysiological exercise tests.

OBJECTIVES: This study aimed to determine the usefulness of electrophysiological exercise tests. The significance of slightly abnormal exercise tests was also examined. METHODS: We identified all the patients who had undergone exercise testing between February 2007 to June 2022 in Tampere University Hospital, Finland. Their medical records after diagnostic workup and exercise test reports were reviewed. A binary logistic regression was performed to evaluate the association between positive test result in short exercise test, long exercise test, or short exercise test with cooling and genetically confirmed skeletal muscle channelopathy or myotonic disorder. RESULTS: We identified 256 patients. 27 patients were diagnosed with nondystrophic myotonia, periodic paralysis, myotonic dystrophy type 1, myotonic dystrophy type 2, or other specified myopathy. 14 patients were suspected to have a skeletal muscle channelopathy, but pathogenic variants could not be identified. The remaining 215 patients were diagnosed with other conditions than skeletal muscle channelopathy or myotonic disorder. The combined sensitivity of exercise tests was 59.3% and specificity 99.1%. Abnormal exercise test result was associated with increased risk of skeletal muscle channelopathy or myotonic disorder (OR 164.3, 95% CI 28.3-954.6, p < 0.001). CONCLUSIONS: Electrophysiological exercise test is not optimal to exclude skeletal muscle channelopathy. It may be useful if a skeletal muscle channelopathy is suspected and genetic testing is negative or indeterminate and further evidence is required. Slightly abnormal exercise test results are possible in various conditions and result from different aetiologies. There is a demand for neurophysiological studies with higher sensitivity to detect skeletal muscle channelopathies.

CACNA1S Variant Associated With a Myalgic Myopathy Phenotype.

BACKGROUND AND OBJECTIVES: This study aimed to characterize the phenotype of a novel myalgic myopathy encountered in a Finnish family. METHODS: Four symptomatic and 3 asymptomatic individuals from 2 generations underwent clinical, neurophysiologic, imaging, and muscle biopsy examinations. Targeted sequencing of all known myopathy genes was performed. RESULTS: A very rare CACNA1S gene variant c.2893G>C (p.E965Q) was identified in the family. The symptomatic patients presented with exercise-induced myalgia, cramping, muscle stiffness, and fatigue and eventually developed muscle weakness. Examinations revealed mild ptosis and unusual muscle hypertrophy in the upper limbs. In the most advanced disease stage, muscle weakness and muscle atrophy of the limbs were evident. In some patients, muscle biopsy showed mild myopathic findings and creatine kinase levels were slightly elevated. DISCUSSION: Myalgia is a very common symptom affecting quality of life. Widespread myalgia may be confused with other myalgic syndromes such as fibromyalgia. In this study, we show that variants in CACNA1S gene may be one cause of severe exercise-induced myalgia.