Inflammatory arthritis: a unique presentation of human anaplasmosis.

Human granulocytic anaplasmosis (HGA) is a tickborne rickettsial disease caused by the bacterium Anaplasma phagocytophilum. Reported cases have increased with the highest incidence in the Northeast. To our knowledge, this is the first report of anaplasmosis associated with an inflammatory arthritis. A 64-year-old man, with a history of Crohn's disease controlled on budesonide, presented to the emergency room in August 2017 with a week history of headache, sore throat, fever, myalgias, rash, and joint pain. There was no clinical evidence of active Crohn's disease. He lives in Nassau County and participates in outdoor activities. His exam was notable for a maculopapular rash over the trunk, arms, and thighs as well as synovitis of several proximal interphalangeal joints. Lab tests revealed transaminitis and elevated inflammatory markers. When evaluated by rheumatology, he had marked polyarthritis of wrists and hands as well as extremely painful motion of the shoulders, elbows, hips, knees, and ankles despite ibuprofen. Prednisone 20 mg daily resulted in significant improvement in his arthritis. Because of an Anaplasma phagocytophilum IgM of 1:320 (normal < 1:20; IgG < 1:64; normal < 1:64) that returned few weeks after presentation, he was prescribed 4 weeks of doxycycline. Convalescent Anaplasma serologies revealed negative IgM and IgG > 1:320. He fully recovered and was able to discontinue steroids. HGA presents acutely with a spectrum of manifestations ranging from a flu-like illness to severe complications such as respiratory failure. Myalgias and arthralgias are common, but an inflammatory arthritis has not been described.