Diagnostic value of lactate dehydrogenase isoenzymes in cerebrospinal fluid

To evaluate the diagnostic value of lactate dehydrogenase (LD) isoenzymes in cerebrospinal fluid (CSF), 93 consecutive CSF specimens were analyzed. These specimens were from patients of four categories: tumors, infections, hemorrhages, and others. It was found that the isoenzyme patterns overlapped among different categories, but they differed within each category and were thus helpful in differential diagnosis. For instance, metastatic tumors showed prominent LD-5, whereas a primary brain tumor demonstrated an increase in all fractions. Viral encephalitis revealed an increase in the first three isoenzymes and bacterial meningitis, the last two. In acquired immune deficiency syndrome (AIDS) cases, however, LD isoenzyme changes were demonstrated in CSF when only cryptococcal meningitis and not when encephalitis was present. Both subdural and subarachnoid hemorrhages showed elevation of all fractions in our study. Elevation of the first three fractions was usually due to brain tissue damage or hemorrhage, as proven by our isoenzyme study of hemolysate mixed with CSF. The prominence of the last two fractions was related to anaerobic metabolism in the central nervous system or to granulocytic infiltration. In conclusion, LD isoenzyme analysis in CSF is helpful in differential diagnosis of various CNS disorders, although its sensitivity awaits further improvement.