Autoimmune-induced focal meningoencephalitis.

We present the case of a male aged 74 years suffering from long-term rheumatoid arthritis with no pharmacological treatment. He visited the emergency department due to sudden loss of strength in both right limbs. In the preceding few months he had experienced asthenia and weight loss due to hyporexia. Physical examination revealed significant joint deformities, mild right hemiparesis with hyperreflexia and right-sided Babinski reflex. His symptoms led us to frame the following differential diagnosis: cerebrovascular disease, intracranial infection or inflammation, neoplasia, or toxic-metabolic disorders. As cerebrovascular disease was the first suspected diagnosis, doctors ordered a blood test (including haemogram, biochemical, coagulation, immunology, tumour markers, and serology studies), an electrocardiogram, a chest radiography, a transcranial vertebrobasilar Doppler ultrasound, carotid duplex scan, and an emergency brain CT. Results from the electrocardiogram, transcranial Doppler and carotid duplex scan were normal. Brain CT showed left subcortical frontoparietal cerebral oedema with leptomeningeal impairment. Complementary test results did not permit us to rule out the aetiologies contemplated in the initial evaluation (neoplasia, intracranial infection or inflammation). We therefore decided to admit the patient and complete an extended diagnostic study. Laboratory analyses revealed an increase in acutephase reactants (fibrinogen 531 mg/dL, ESR 62, CRP 105.78 mg/dL), high titres of rheumatoid factor (RF 2770), and elevated serum immunoglobulins (IgG 602, IgM 230). Tumour markers were normal and serological tests for HBV, HCV, CMV, and HIV were negative. Lumbar puncture revealed intrathecal synthesis of IgM with biochemical analyses, cytology, and CSF culture all being normal. Brain MRI was indicative of leptomeningeal impairment (Fig. 1) with a predominantly left posterior and parietal subcortical oedema (Fig. 1B) suggesting meningoencephalitis. There were no signs on the PET-CT suggesting viable tumour tissue at any level. The most likely aetiology based on these findings is autoimmune focal encephalitis related to the patient’s underlying disease. Doctors suggested performing a brain biopsy, but the patient and his family refused the procedure. Doctors therefore began treatment with prednisone (1 mg/kg/day). At 15 days after the onset of intravenous corticosteroid treatment, the patient presented no neurological symptoms. He was then started on immunosuppressants to specifically treat his disorder.