Background Systemic Lupus Erythematosus (SLE) patients are known to be prone to infections. In particular differential diagnosis between an acute infection or a disease flare should be performed in any SLE patient with fever or recurrent fever and signs of acute disease. Differential diagnosis becomes even more difficult in an SLE patient with central nervous system (CNS) involvement. The aim was to describe an SLE patient with CNS involvement and acute West Nile virus infection.

Methods A female patient was diagnosed with SLE at the age of 32 with a light-sensitive face eruption, hair loss, fatigue, arthralgias, ANA 1/320 (+) and anti-dsDNA (+). At the age of 45 she developed CNS involvement with epileptic seizures, dysarthria, memory loss, concentration difficulties and an abnormal EEG. At the age of 53 she had an acute SLE flare and pulse cyclophosphamide iv was administered. Thereafter rituximab was given followed by hydroxychloroquine and prednisolone 10 mg/d. At the age of 54 years 3 months after the third rituximab cycle, while on therapy with hydroxychloroquine and prednisolone she developed diarrhea, vomiting and fever up to 40°C not responding to antipyretics. She presented to the emergency department with deteriorating renal function, fever and confusion.

Results A brain MRI showed meningeal thickening and a lumbar puncture was performed. The diagnostic evaluation of the fluid aspirated showed a recent infection with the West Nile virus with IgM (+++) in serum and IgM (+) in the cerebrospinal fluid. Two weeks later the patient had improved, was oriented in place and time and had no focal neurological signs.

Conclusions Patients with SLE are prone to infection, especially if they are on long-standing treatment with steroids. Whenever they present with signs of acute disease they should be carefully evaluated for the presence of an acute infection, as infections demand a different therapeutic approach to a disease flare. A patient with CNS involvement demands even more careful and extensive evaluation. The presence of West Nile virus in Europe in recent years along with other mosquito-borne viruses have created new diagnostic and therapeutic challenges in the management of immunosuppressed patients, as was the case in the patient presented herein.