A 56-year-old male with a past medical history of seronegative rheumatoid arthritis (treated with abatacept 1000 mg every 4 weeks and sulfasalazine), neuropathy, obstructive sleep apnea and prior right hip arthroplasty completed 9 years previously in the setting of avascular necrosis, presented to clinic with a 3-month history of malaise and low-grade temperature of 99 F. He had returned from a mission trip to Honduras 3 months previously. He initially developed a low-grade temperature 1 month after returning, which was followed by unintentional weight loss and night sweats. He had mild congestion and took a course of amoxicillin without improvement in temperature or night sweats. Subsequently, he developed progressive right hip pain. A bone scan was unremarkable. A fever of 103 F prompted hospital admission for evaluation.
The patient reported no additional symptoms at the time of admission and his abatacept was held. He reported drinking only bottled water in Honduras with no adventurous eating. He was born in California but had lived in the Midwest United States much of his life. He is married, monogamous, and had no history of tobacco or recreational drug use. He had traveled to Mexico previously but denied other recent travel. He reported no tuberculosis or animal exposures.
On examination, extremities were atraumatic without synovitis. He had mild discomfort with internal rotation of the right hip. The examination was otherwise unremarkable. Laboratory evaluation revealed a white blood cell count (WBC) of 6.3 K/UL (normal 4.5 - 11.0 K/UL) and hemoglobin of 12.4 grams (normal 13.5 - 16.5 gm/dL). Erythrocyte sedimentation rate (ESR) was 25 mm/h (normal < 20 mm/hr). Liver transaminases were normal. The following infection diagnostics were negative: malaria smear and Ag, HIV ag/Ab, Syphilis Ab, Histoplasma serum Ag and Ab, Coccidiodes serology, Cryptococcal serum Ag, Bartonella and Brucella IgG/IgM, T spot TB, Chikungunya IgG and 2 sets of blood cultures. A chest radiograph and echocardiogram were unremarkable. A 2-view hip radiograph demonstrated right hip arthroplasty without periprosthetic lucency or fracture. The patient underwent a tagged white blood cell scan, which did not demonstrate any increased uptake (Figure 1). An MRI scan of the right hip joint without contrast demonstrated fluid collections medial to the lesser trochanter, consistent with hematoma or pseudotumor (Figure 2). Joint aspirate was grossly purulent. The patient was taken to the operating room for prosthetic explant with antibiotic spacer placement. Antibiotic spacer was ceramic total hip system, which was cemented in with antibiotic-impregnated cement with 5g of Vancomycin and 1.2g of Gentamicin.
Testing from the operated room revealed that the joint aspirate cell count was unreadable as the cells were degenerated. Gram stain of the aspirate was negative for microorganisms. Aspirate routine culture was negative, with no growth at 5 days on aerobic and anaerobic culture. Aspirate grew acid-fast bacteria at 10 days, identified later as MAC. Fungal cultures remained negative. Tissue cultures including femoral head component had negative routine culture and fungal culture. AFB culture of the tissue grew MAC. Blood cultures were negative for mycobacteria at 6 weeks. Macrolide sensitivities were performed and the isolate was found to be clarithromycin susceptible.
Initial broad-spectrum antibiotics were adjusted and he was discharged on intravenous amikacin three times weekly with oral rifampin, ethambutol, and azithromycin. Amikacin was discontinued after 4 weeks of treatment. The remainder of antimicrobial therapy was continued for 12 months. The patient's rheumatoid arthritis treatment included sulfasalazine and hydroxychloroquine, resumed after 3 months of antimicrobial treatment. He started methotrexate treatment 6 months after starting antimicrobial therapy for better joint pain control. Eleven months after treatment initiation, repeat joint aspiration culture was negative. He underwent repeat right THA and tissue cultures were negative. One year following the revision THA he remains free of infection. To date, he remains off biologic immunosuppression.