A Differential Diagnosis of Drug-Induced Aseptic Meningitis

A septic meningitis refers to a nonbacterial inflammation of the leptomeninges.1 Viruses are the most common cause of aseptic meningitis, and the most common viruses that cause aseptic meningitis are enteroviruses. Drug-induced aseptic meningitis is rare but probably more common than the literature would suggest; therefore, it should be included in the differential diagnosis of aseptic meningitis, particularly if aseptic meningitis develops in association with the use of NSAIDs or other offending drugs (Table 1) and if clinical recovery is rapid following cessation of the drug or if results of viral studies are negative. The pathogenetic mechanisms of drug-induced aseptic meningitis are not fully understood, but 2 major mechanisms have been proposed. One proposed mechanism is that the meninges are directly irritated by the intrathecal administration of drugs. The other is that the meninges are expressing an immunological hypersensitivity—most often a type 3 or type 4 hypersensitivity reaction—to the offending drug.2 An association between hypersensitivity reactions and underlying collagen-vascular disease or rheumatological disease has been reported.1-10 Typically, the cerebrospinal fluid (CSF) profile in drug-induced aseptic meningitis is that of a neutrophilic pleocytosis accompanied by a normal CSF lactic acid level and a variably elevated CSF protein level.1,3 Patients who have druginduced meningitis may have eosinophils present in the CSF (fewer than 5%).