Rare manifestation of initial central nervous system involvement in severe fever with thrombocytopenia syndrome-associated encephalopathy/encephalitis: a case report.

Severe fever with thrombocytopenia syndrome (SFTS) is a potentially fatal infectious disease if not diagnosed and treated promptly. Typical clinical features include fever, thrombocytopenia, and lymphadenopathy. However, we encountered a case of SFTS in a 60-year-old male who initially did not exhibit these hallmark symptoms. The patient presented with headache and myalgia, but fever did not develop until the 4th day of hospitalization. Initial neuroimaging and cerebrospinal fluid (CSF) analysis revealed no abnormalities. When the fever emerged, follow-up imaging revealed findings consistent with meningitis as a complication of SFTS. The patient was successfully treated with antibiotics and made a full recovery. This case underscores the challenges in diagnosing SFTS in patients who lack fever, CSF pleocytosis, or typical neuroimaging findings at presentation. Additionally, it highlights the importance of differentiating SFTS-related meningitis from other causes of encephalitis to avoid inappropriate treatments, such as immunosuppressive therapy, which could worsen viral infections.