NEUROPATHOLOGIC APPLICATIONS OF IMMUNOHISTOCHEMICAL FIBER TYPING IN THE NON-NEOPLASMS MUSCLE BIOPSY

The determination of fiber types is routinely accomplished in skeletal muscle biopsy specimens by enzymatic histochemical analysis, which de tects adenosine triphosphatase (ATPase) activity on cryostat sections. This study assesses postmortem antigen degradation, the effects of fi xation and processing, and the nueropathologic applications of MY-32, a monoclonal antibody to fast twitch skeletal myosin. Formalin-fixed, paraffin-embedded sections of skeletal muscle biopsy specimens obtaine d from the quadriceps femoris were immunoreacted with this antibody. C ryostat sections of the same muscle biopsy specimens were examined aft er brief fixation in either acetone or formalin. Parallel cryostat sec tions of frozen muscle were also assessed with ATPase preparations at pH 9.4 and 4.3. To evaluate the effect of postmortem interval and auto lysis on antigen degradation, skeletal muscle samples obtained at 12 h ours postmortem were immunoreacted after 12, 24, or 36 additional hour s. These specimens were examined as immunoreacted cryostat sections an d compared with parallel sections reacted for ATPase at Ph 9.4 and 4.3 . Representative sections from each time point were also fixed in form alin, routinely processed, paraffin embedded, and immunoreacted. Selec ted muscle biopsy specimens with a range of neuropathologic diagnosis, including fiber type grouping, Type II atrophy, and congenital fiber type disproportion, were also assessed for immunoreactivity. Our resul ts indicate that the MY-32 monoclonal antibody specifically reacts wit h Type II (fast twitch) fibers. Immunoreactivity is most intense in cr yostat sections immersion fixed in acetone, but moderately intense, sp ecific immunoreactivity can be clearly identified in formalin-fixed (f rozen or paraffin-embedded) tissue obtained even 48 hours after death. Application of this nonenzymatic method for fiber type determinations in the neuropathologic evaluation of skeletal muscle biopsies is pres ented.