A case of acute monocytic ehrlichiosis with prominent neurologic signs.

Human monocytic ehrlichiosis is a recently described tick-borne infection with the rickettsial organism Ehrlichia chaffeensis. We describe a patient with documented E chaffeensis infection and multiple organ system involvement. Prominent neurologic symptoms and signs included severe headache, meningismus, and altered mental status. Additional neurologic findings included unilateral arm weakness and a Bell's palsy. Biopsy of brain and meninges demonstrated an infiltrate of atypical lymphoid cells in the leptomeninges with involvement of blood vessel walls and extension into the Virchow-Robin spaces. Bone marrow biopsy revealed fibrin-ringed granulomas. The patient also developed a nonspecific increase in immunoglobulin production. Host immune response may play a critical role in the pathophysiology of ehrlichiosis.