Rapidly progressive dementias (RPD) are conditions that develop over days, weeks or months, which could be treatable if diagnosed in the acute phase.

A 62-year-old man with personal history of type 2 diabetes, started complaining of fronto-temporal headache, nausea and sub-febrile temperature. He went to his family doctor who prescribed ciprofloxacin 500mg bid. Later on, he had difficulty to sleep and referred complex visual hallucinations. His family noted involuntary movements of the left upper limb and that he became more clumsy needing help for daily life activities. He went to our hospital one week later. He was apyretic and hemodynamically stable. On neurological examination, he had executive and visuospecial dysfunction, left limbs bradykinesia and ipsilateral limb ataxia. Involuntary movements of his left upper limb resembled alien limb phenomena. Complete blood count, complete metabolic panel, iron, folic acid, vitamin B12, anti-neuronal antibodies were normal. HIV, hepatitis B and C serologies were negative. Cerebrospinal fluid study showed 4 cells (100% mononuclear), normal glucose and protein levels, negative bacteriological exam but positive Herpes Simplex-1 Virus (HSV) DNA. Brain CT and MRI showed signs of ischemic microangiopathic leukoencephalopathy. He started treatment with acyclovir 30mg/kg/d IV and quetiapine 100mg id. His symptoms improved but he remained with a mild mnesic cognitive deficit and bradykinesia that stayed stable 3 years later.

This case exemplifies atypical HSV-1 encephalitis, one cause of RPD, that an early recognition is essential to reduce its associated morbidity.