Myopathies diagnosis

Although clinical examination provides important clues to diagnosis of congenital myopathies, ultrastructural and histochemical examination of muscle biopsies provides the key to definitive identification. Most of the congenital myopathies... 

Phosphorus-31 MRS has been used widely to investigate mitochondria diseases in muscle. Trenell et al. measured an elevated ADP concentration and pHi in a group of mitochondrial myopathy (MM) patients, which is evidence of impaired oxidative ATP production in their skeletal mus-cle This study also showed that increased inspired oxygen concentration improves oxidative fimction in MM patients. In a separate study, Jeppesen et al. could not differentiate healthy subjects and MM patients using P MRS. ° They concluded the P MRS should not be a routine test in the diagnosis for MM patients. 

Biopsy is not justified as a routine, but it is useful as a diagnostic tool in distinguishing suspected corticoid myopathy from diseases of the muscles or vascular system with inflammation that may have been the indication for giving glucocorticoids in the first place electromyographic measurements cannot confirm the diagnosis. 

Diagnosis of mitochondrial myopathies is initially clinical, involving phenotypic (observable expression of characters and traits) evaluation, followed by laboratory evaluation. If an mtDNA mutation is detected, diagnosis is relatively straightforward in the absence of an mtDNA mutation, diagnosis becomes difficult. Laboratory studies may include blood plasma or cerebral spinal fluid measurement for lactic acid, ketone bodies, plasma acylcarnitines and organic acids in the urine. If they are abnormal, a muscle biopsy is performed. 

Hanisch, F., Neudecker, S., Wehnert, M. and Zierz, S. (2002) Hauptmann-Thannhauser muscular dystrophy and differential diagnosis of myopathies associated with contractures. Nervenarzt 73, 1004-1011. 

Continuous refinement has brought the use of serum enzymology in the diagnosis of myopathy to a high degree of reliability, so that, by careful interpretation of results, important information may quickly be... 

Chariot P, Monnet I, Mouchet M, Rohr M, Lefaucheur JP, Dubreuil-Lemaire ML, et al. Determination of the blood lactate pyruvate ratio as a non-invasive test for the diagnosis of zidovudine myopathy. Arthritis Rheum 1994 37 583-6. 

Comprehensive investigation into thyroid-associated eye disorders includes thyroid function and antibody panels. Acetylcholine receptor antibody titers and autoimmune screen are recommended if available. Muscle enzyme levels and serum lactate assays will be helpful in the diagnosis of myopathy. 

Electromyography (EMG) involves evaluation of the electrical activity of the muscle with the insertion of a concentric needle. The pattern of electrical signals provides information for the diagnosis of neuropathy or myopathy, its chronicity and localization (Figure 112.1). 

Fatty acid oxidation disorders should be considered in any case of unexplained hypoglycemia and/or myopathy. The laboratory diagnosis relies on the measurement of plasma acylcarnitines and urine organic acids, mainly the alternative fatty acid oxidation products. Novel defects may be expected to be delineated, especially the short- and medium-chain enzymes have not... 

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