A 24-year-old, Vietnamese male, living in Switzerland for the last three years, consulted our unit for unremitting pain in his right knee. He had a right knee contusion two months ago. On history, he related occasional night sweats with chills since that accident accompanied with a weight loss of 5 kg. Otherwise, he is in good health, does not smoke, and takes no medications.
Clinical examination showed a painful red nonulcerating indurations measuring 3 x 4 cm in surface at the level of the right fibular head. It is fluctuating and seems to be adherent to the deep subcutaneous plane. Right knee mobilisation was complete, and neurovascular examination was normal. Blood analysis revealed a marked microcytic anaemia (haemoglobin: 76 g/L, VGM: 61 fl), no leukocytosis, and a CRP of 4 mg/L. Knee radiography showed a lytic lesion with ill-defined margin in the proximal right fibula measuring 1 x 1 cm and breaking through the outer cortex (Figure 1(a)). We reserved the differential diagnosis of focal osteomyelitis versus a tumoral process since the radiography showed that progressive lesion (Figure 1(b)). MRI examination demonstrated a hypersignal on T2 images of the proximal right fibular head with breakage through the outer cortical bone and an abscess extension in the surrounding soft tissues. This excluded the tumoral process as a causal agent and oriented us to a focal osteomyelitis with local infiltration of peripheral tissues (Figure 2). Surgical debridement was done through a centred lateral incision and tissue fragments sent for bacteriology and path anatomy analysis with a special request to look for tuberculous infection. This atypical request was based on the ethnical origin of the patient and the lytic lesion on radiography. Antibiotic therapy has been started empirically with Augmentin (amoxicillin and clavulanic acid) at a dose of 2, 2 g intravenous three times a day. The path anatomical analysis revealed the presence of an acid-alcohol resistant bacillus within an inflammatory process. Bacteriological results were noncontributive. A mycobacterium infection as the source of the osteomyelitis is suggested, but the IDR (intradermal reaction to tuberculin) tuberculosis test came out negative after 72 hours.
Locally, scar adhesion developed, a second surgical debridement was done, and new bone and tissue fragments were sent for bacteriology and molecular biology for analysis in order to identify the type of mycobacterium.
In the meanwhile, we completed and widened our investigations looking for any signs of immunodepression. Our results confirmed the presence of an HIV infection diagnosed as AIDS with a CD4 count less than 65/mm3 and a CD4/CD8 ratio of 0.035. It also revealed the presence of a viral hepatitis C infection. An antipneumocystic prophylaxis with Bactrim Forte (1 pill three times a week) was started. PCR (polymerase chain reaction) results of the last fragments analysed show the presence of an atypical nontuberculous mycobacterium identified as Mycobacterium haemophilum. Antimycobacterial treatment with Clarithromycin (500 mg/day), Moxifloxacine (400 mg/day), and Rifabutin (300 mg/day) was started for a minimum of 12 months. Secondarily, an antiretroviral treatment was started 2 weeks later. Locally, the patient is doing now well and is treated by our infectious disease department team for further followup and control.