The distribution and intensity of
alkaline phosphatase deposition in 54 patients with
dermatomyositis-
polymyositis (PM-DM) was analyzed by the
enzyme histochemical method. Increased
enzyme reactivity of endomysial capillaries was found in 28% of patients, equally distributed between adult onset PM (Group I) and PM-DM with overlap in other
connective tissue diseases (Group V). Patients with high endomysial capillary reactivity (R1 larger than or equal to 60) responded poorly to
steroids, had an increased incidence of
rheumatoid factor, and had less fiber degeneration/
necrosis in their biopsies. Twenty-two percent of patients demonstrated prominent perimysial
phosphatase reactivity localized in newly formed
collagen and fibroblasts. Thirty patients (55%) demonstrated significant numbers of
alkaline-phosphatase-positive fibers positively correlated with increased fiber degeneration/
necrosis, endomysial
fibrosis, increased numbers of
triglyceride-containing muscle fibers, and
NADH tetrazolium reductase hyperreactivity. Minimal overlap between the three
enzyme distribution patterns was found. Endomysial capillary activity probably represents endothelial
alkaline phosphatase induction analogous to the pattern seen normally in lower mammals (rat, rabbit, guinea pig).
Alkaline phosphatase fiber reactivity probably represents a particular phase in fiber regeneration/maturation especially after
denervation and is positively correlated with an increased incidence of spontaneous fibrillation potentials in PM-DM.