Background General paresis (GP) is a late form of parenchymal neurosyphilis causing dementia and neuropsychiatric disorders. The diagnosis is often difficult since the clinical signs are protean. So far, neuroimaging has played a minor role as radiological findings are not specific.

Methods We studied three immunocompetent patients, admitted to hospital for cognitive impairment. The diagnosis of neurosyphilis was formulated on the basis of serological texts and cerebrospinal fluid analysis. The patients underwent a 3 T MR examination including susceptibility-weighted imaging (SWI) sequence before and after the initiation of penicillin therapy.

Results In all patients, SWI revealed cortical hypointensity, mostly distributed in frontal and temporal lobes. In drug-naive patients, the hypointensity extended over the whole cortical thickness, from the cortical/subcortical junction to the pial surface. After starting the penicillin therapy, the cortical hypointensity partially reversed, involving only the deep cortical layers.

Conclusions The MRI pattern at SWI observed in patients with GP was not reported in other infectious or inflammatory disease of the central nervous system, thus we suggest it could be a peculiar radiological finding of the disease. On the basis of previous pathological data, we hypothesise that cortical SWI hypointensity could be expression of iron deposits within activated microglia.