Diagnosis of meningeal involvement in patients with acute lymphoblastic leukemia: immunofluorescence for terminal transferase.

As indirect immunofluorescence technique (I) for detecting TdT enzyme was used to study leukocytes present in the cerebrospinal fluid (CSF) of patients with documented acute lymphoblastic leukemia, nonlymphoid leukemias, and unrelated nonmalignant disorders. TdT was found to be expressed in all cases of overt meningeal lymphoblastic leukemia studied but was absent from leukocytes in patients with nonlymphoid leukemia and lymphocytic meningitis. In addition, the IF test proved useful in identifying leukemic blasts in CSF where these were of atypical morphology or present in extremely low numbers. Immunofluorescence for TdT is a useful tumor marker in the CSF of patients with ALL.