Systemic Sarcoidosis Mimicking a Behavioural Variant of Frontotemporal Dementia

Among rare neurological manifestations, a progressive dementia may exceptionally be the revealing clinical feature of a sarcoidosis. Diagnosis may then be difficult, especially when systemic signs are missing or latent, with a risk of therapeutic delay. We report the first case of sarcoidosis mimicking a frontotemporal dementia. A 53-year-old man presented with a dementia clinically suggestive of frontotemporal dementia, progressing slowly for about 2 years. However, MRI revealed unusual aspects, mainly large areas of T2/FLAIR hypersignal within temporal regions and cerebellum, with nodular leptomeningeal and juxtacortical Gadolinium enhancement. The patient was finally diagnosed with a systemic sarcoidosis. We discuss the differential diagnosis based on MRI aspects and review the literature on the clinical, biological, and imaging features of sarcoidosis presenting with dementia. This case demonstrates that brain imaging remains mandatory in the exploration process of a patient with dementia. Although the patient presented with rather typical features of a behavioural variant of frontotemporal dementia, the MRI aspect was the key exploration that leaded to the diagnosis.