Abstract

Type 2 fiber predominance or a decrease of the type 1/type 2 ratio was rarely reported as the only abnormal pathologic finding in patients suffering from muscle cramp and myalgia. Here, we describe the clinicopathologic findings of three cases of type 2 fiber predominance, presented with muscle cramp and myalgia in otherwise healthy patients. All of them were young men (18, 19 and 22 years). Light microscopic and neurologic examinations, and laboratory data showed mere nonspecific findings that were not concordant with their subjective symptoms. However, enzyme histochemistry performed on muscle biopsy revealed an increased fraction of type 2 fibers; 73%, 80%, and 75%, in each case. The pathogenesis of this entity remains unclear, but the recognition of this unusual clinicopathologic entity is important for both pathologists and neurologists so they can avoid misdiagnoses or unnecessarily tiresome studies. We emphasize that type 2 fiber predominance should be included in the underlying causes of unexplained muscle cramps and exertional myalgia, especially among young adults, although it remains unclear whether the fiber type predominance is a separate entity or a part of other underlying neurologic or systemic disorders.

• Keywords: Muscle Cramp;Exertion;Muscle Fibers;Predominance;Myalgia;