Congenital and metabolic myopathies of childhood or adult onset

Muscular glycogen storage diseases without increased glycogen content on histopathological examination

Histopathological findings of muscle biopsies from five patients with two different muscular glycogen storage diseases (mGSD) were presented. From these investigations it emerged that the yield of histopathology in mGSD is low. In only one of five patients histopathological findings gave a clue towards diagnosis. It can be concluded that non-specific findings or even normal appearance of a muscle biopsy does not exclude mGSD.

[Analysis of 12 cases of McArdle's disease diagnosed after 30 years]

PURPOSE

McArdle's disease (MAD) or glycogen storage disease type V, usually starts in childhood or adolescence. Generally diagnosis is made before the early adulthood because patients present well defined syndrome and are constrained.

METHOD

We retrospectively investigated all MAD cases diagnosed in the biochemical laboratory from Debrousse Hospital in Lyon, during 40 years (1962-2002). We then selected patients whose diagnosis had been made after 30 years.

RESULTS

Fifteen patients answered our criteria but only 11 files could be analysed. A twelfth patient (service of internal medicine--Royan) supplemented the series. We sought the reasons of a late diagnosis: early age of beginning but few symptoms (7 cases), age of beginning higher than 20 years (5 cases including 3 after 45 years). The principal symptoms were muscular deficit and muscular pains (8 cases) and second wind phenomenon (7 cases). Creatinine phosphokinase level was constantly high. Ischemic effort test when it was carried out was constantly abnormal. Conversely electromyogram was often normal (5 cases). Several biopsies were necessary in a third of the cases to evoke the diagnosis, particularly among the patients with late onset symptoms.

CONCLUSION

Diagnosis of metabolic MAD is generally easy if the interrogation finds inaugural symptoms in childhood or adolescence even if the patient consults very late in the life. The diagnosis can become much more difficult if it begins late in life (atypical symptoms, need for several muscular biopsy).

Differentiating idiopathic inflammatory myopathies from metabolic myopathies

The metabolic myopathies are a heterogeneous group of diseases, including glycogenoses, disorders of lipid metabolism, and mitochondrial myopathies, that result primarily from inborn errors of metabolism. Most of these metabolic defects cause medical conditions that manifest early in life. Nevertheless, clinical presentations during the teenage years and adulthood are increasingly being recognized. Many of the clinical manifestations of these diseases are difficult to differentiate from those observed in the idiopathic inflammatory myopathies, especially polymyositis. A directed evaluation using the clinical, laboratory, and genetic approaches summarized in this article, however, should allow for the differentiation of most metabolic myopathies from polymyositis and other forms of idiopathic inflammatory myopathy. The diagnosis of a metabolic myopathy should be considered in patients who appear to have polymyositis but lack the characteristic changes of inflammation found on EMG, MRI, or muscle histology, or in such patients who are refractory to immunosuppressive therapy. The forearm ischemic exercise test is especially useful to screen for some inborn errors of glycogen metabolism or glycolysis and for myoadenylate deaminase deficiency. Thorough analysis of muscle tissue, including histology, histochemistry, biochemistry, and occasionally electron microscopy, is often necessary to make the diagnosis of a metabolic myopathy. Advances in molecular biology methods and knowledge of the precise genetic defects associated with these metabolic defects are dramatically increasing our capacity to diagnose patients with a widening range of myopathies. It is expected that, with further understanding of the mechanisms of the metabolic and idiopathic inflammatory myopathies, the differentiation of these disorders into their pathogenetic components, and the capacity to diagnose them will continue to improve. These are essential factors in improving genetic counseling and eventually the therapy of these serious, and currently incurable, disorders.

Muscle diseases in elders: a 10-year retrospective study

BACKGROUND

Muscle complaints are frequent among older adults, but histological data in this setting are scarce. Our objective was to detect the major categories of muscle diseases in the elderly population based on histological study.

METHODS

We reviewed all muscle biopsies performed in our hospital on patients older than the age of 65 during a 10-year period (1988-1997). As a control group, we included the next patient younger than 65 who underwent muscle biopsy after each elderly patient. We recorded demographic, clinical, and histological data of the patients, as well as the final diagnosis. Concordance between pre- and postbiopsy diagnosis was also analyzed.

RESULTS

We included 239 muscle biopsies corresponding to elderly patients and 239 to controls. Compared with the control group, elderly patients more frequently exhibited type II fiber atrophy and were diagnosed with a specific myopathy. The latter was achieved in 86 cases (36%), idiopathic inflammatory myopathies and vasculitis being the most frequent diagnoses. Interestingly, in about one quarter of the elderly patients in whom a definite diagnosis of muscle disease was achieved, this diagnosis had not been clinically suspected prior to muscle biopsy. Overall, in 60 out of 239 elderly patients (25%), a specific therapeutic regimen could be instituted on the basis of the muscle biopsy results.

CONCLUSIONS

Muscle diseases are not rare in elderly patients. Therefore, muscle biopsy constitutes a safe and useful tool for diagnosis because, if not performed, some potentially treatable diseases may be undiagnosed or misdiagnosed.

The clinical laboratory evaluation of the patient with noninflammatory myopathy

The investigations used to diagnose an inflammatory muscle disease include history and physical examination, evaluation of serum levels of enzymes derived from skeletal muscle, electromyography, magnetic resonance imaging, and muscle histology. The evaluation of patients who may have noninflammatory myopathy includes, but is not limited to, these methods. Additional tools that may be useful include measurements of additional biochemistries, the forearm ischemic exercise test, magnetic resonance spectroscopy, and special tests on muscle tissue. Reports published in the past year have improved and expanded our understanding of the numerous noninflammatory myopathies and how these tools can be used more effectively.