Lactic dehydrogenase isoenzymes in the cerebrospinal fluid of patients with systemic cancer

Lactic dehydrogenase (LDH) isoenzymes were measured in the cerebrospinal fluid (CSF) in a group of patients suffering a variety of cancer‐related neurologic problems. LDH‐5 isoenzyme as a percentage of total LDH activity was abnormally elevated (above 10 to 15%) in leptomeningeal infiltration by carcinoma (breast carcinoma, lung carcinoma, and malignant melanoma) but not in other types of CNS metastases. Abnormal LDH isoenzyme patterns were also seen with CSF infections in which a granulocytic pleocytosis was present. In the absence of infection, an elevated LDH isoenzyme 5:1 ratio suggested leptomeningeal tumor and, when used with other CSF markers (beta‐glucuronidase and CEA), LDH isoenzymes aid in early detection of this metastatic neoplastic process. They may also help to differentiate leptomeningeal tumor from other chronic meningitides. Measurement of CSF markers also aids in assessing the effectiveness of treatment since marker levels often vary with the clinical course.