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Pitfalls in Muscle Biopsies of Hypotonic Children

MUSCLE biopsy interpretation of questionable neuromuscular disease in infants and children is frequently erroneous unless the child and his biopsy are reviewed together. A biopsy ordered by one consultant, obtained by a second and interpreted by a third leaves much room for diagnostic error. The highest degree of accuracy in diagnosis is achieved by having the same consultant examine the infant or child and review the muscle biopsy. In this way, artifacts can be recognized and not reported as evidence of neuromuscular disease by a pathologist who has neither examined the child nor had the training to diagnose the clinical picture. Artifacts within muscle are too frequently recorded by pathologists as indicative of neuromuscular disease. This is particularly true in sick newborns. The problem is becoming more acute as many more newborns are surviving today due to the skill of neonatologists. Frequently, muscle biopsies are ordered in intensive care nurseries as part of a routine work-up for a hypotonic, sick infant. If this practice is followed, then changes due to the pathological state of the infant may be interpreted as pathological in the muscle itself: Generally, a muscle biopsy can and should be delayed until the condition of an infant is stable and he is out of the intensive care unit. The indications for a muscle biopsy must be clearly established and should be as follows: (1) There should be a strong suspicion of a neuromuscular disease in the infant or child before a muscle biopsy is ordered. (2) A muscle biopsy should not be obtained as part of a ‘screening’ group of neurological tests, but a clear indication for the biopsy must be established. Otherwise, an erroneous diagnosis may be made by a pathologist and then accepted as a final diagnosis by the clinician. (3) If the problem appears to be one clearly of central nervous system etiology, the indications for a muscle biopsy should be more specific. Artifacts may be seen in biopsies of hypotonic infants with central nervous system pathology, and interpreted as indicative of neuromuscular disease. Muscle biopsies are still being done in the majority of hospitals in the world in a somewhat archaic manner; i.e. they are first immersed in formalin and then embedded in paraffin. Many disorders, such as the congenital myopathies, will be missed without the special histochemical stains which can only be done on frozen tissue. In most hospitals, muscle biopsies are generally processed and interpreted in r-’