Managing psychotic depression and diagnostic uncertainty in liaison psychiatry.

A middle-aged woman presented with a history of symptoms of depression with psychotic features severely affecting her physical health. Neuroimaging of her brain suggested pathological changes out of keeping with her age, leading to further investigations including genetic testing for cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis was also considered as a differential diagnosis as an initial serum test for anti-NMDAR autoantibodies was positive. Her symptoms resolved following treatment with electroconvulsive therapy. Despite her initial neuroimaging, her genetic test for CADASIL was negative and her subsequent test for anti-NMDAR autoantibodies was negative, suggesting that the initial test may have been a false positive.