Serum lactate dehydrogenase isoenzymes in neuromuscular diseases

Serum LDH isozymes render qualitative information which may be more specific than the quantitative changes of total serum LDH and total serum CPK in neuromuscular diseases. Muscle LDH isozymes vary with age, muscle, and species. Temporal study of serum LDH isozymes in experimental neurogenic atrophy demonstrated a temporary rise of serum LDH 5. In acute and progressive neurogenic diseases, a high serum LDH 5 was noted. Isozyme patterns were normal in chronic and non-progressive diseases. In Duchenne dystrophy, serum LDH 5 was low and stayed low until the final stages of the disease. This abnormality persisted long after serum total LDH and CPK returned to normal. This may reflect the leakage of genetically abnormal isozymes from the muscles to serum. It is concluded that the serum LDH isozyme pattern is a reliable qualitative test in the diagnosis of a genetic myopathy, and in differentiating progressive from static neurogenic atrophies.