Cerebrospinal fluid gastrin releasing peptide in the diagnosis of leptomeningeal metastases from small cell carcinoma.

BACKGROUND: The clinical diagnosis of leptomeningeal metastases is often difficult to substantiate. Patients with an underlying malignancy typically present with neurologic symptoms referable to multiple levels of the neuraxis. Although most patients have an abnormal cerebrospinal fluid (CSF), less than 60% have evidence of malignant cells on cytologic examination from a single lumbar puncture, and the disease is usually advanced in patients with positive results. An elevated serum level of gastrin releasing peptide (GRP) in patients with small cell carcinoma has emerged as one of the most useful markers for disease activity.

METHODS: A patient with small cell carcinoma presented with signs of meningitis and an abnormal CSF. However, the CSF gave repeatedly negative cytologic results. Hence, serum and CSF were analyzed for GRP.

RESULTS: The CSF GRP level was elevated by more than six orders of magnitude above the serum level. An autopsy demonstrated extensive meningeal and parenchymal brain involvement by small cell carcinoma.

CONCLUSIONS: The diagnosis of leptomeningeal metastases in patients with small cell carcinoma can be established by CSF GRP testing, even when cytologic examination is negative.