An image analysis study of vastus lateralis muscle fibers in malignant hyperthermia susceptible patients.

We studied the correlation between the in vitro contracture test (IVCT) performed in malignant hyperthermia (MH) and the muscle fiber type composition in 29 human vastus lateralis (VL) biopsy samples (from 12 women and 17 men) using a semiautomated image analyzer. Relative number, lesser diameter, global area, and spatial distribution of the muscle fibers were measured. In these and in 26 additional VL muscle biopsy samples of patients with other myopathies, we compared our morphometric data with the observations made by the pathologist. Among the MH group, type 1 fibers were larger in both malignant hyperthermia susceptible (MHS) men and women reaching statistical significance only in the latter. The relative number and global area were unchanged. In MHS patients relative number and global area of type 2A fibers were smaller. No changes in the parameters of type 2B fibers were found. In a minority of sections (14%) clustering was observed. Sex-related alterations in type 2 fiber characteristics were found between MHS patients. However, our findings do not clearly point towards a syndrome-induced alteration of size, number, global area, or distribution of type 1, 2A, and 2B muscle fibers in VL of MH patients. By morphometric analysis, we found several additional biopsy samples that met the interpretation of "abnormal" size and number of muscle fibers in human malignant hyperthermia than were reported by the pathologist.