Cerebral syphilitic gumma mimicking a brain tumor that enlarged temporarily after commencing antibiotic treatment

In this case report, we describe a 60-year-old man who presented with headaches for 1 year and mild confusion for 3 weeks and was initially diagnosed as having a cerebral tumor on the basis of finding a round lesion in the right lenticular nucleus with ring enhancement on gadolinium-enhanced T1-weighted brain magnetic resonance imaging. However, the discovery of positive serology for Treponema pallidum infection on routine tests on admission prompted analysis of cerebrospinal fluid, which was also positive on Treponema pallidum hemagglutination (TPHA), rapid plasma reagin (RPR), and treponemal antibody absorption (FTA-ABS) tests. Thus, he was diagnosed as having an intracranial syphilitic gumma. After commencing treatment with penicillin G, the lesion temporarily increased in size, but subsequently resolved completely with continuing antibiotic treatment. In the present era of increasing prevalence of syphilitic infection and because they are eminently treatable, syphilitic gummas should be included in the differential diagnosis of apparent brain tumors. Additionally, temporary enlargement of a probable gumma after instituting antibiotic treatment should not prompt cessation or change of the antibiotics.