A 78-year-old diabetic and hypertensive male patient, presented with pain, swelling and discharging sinuses in both knees, 5 weeks after sequential bilateral TKR at a peripheral hospital, with no response to cloxacillin and ofloxacin. Discharge revealed acid-fast bacilli (AFB), but was negative for cartridge-based-nucleic-acid-amplification test (Xpert MTB/Rif). Empirical anti-tubercular therapy (ATT) was initiated, (rifampin, isoniazid, pyrazinamide and ethambutol) with minimal response, stopped after seven months, followed by bilateral knee debridement and poly-exchange but the discharge continued.
Eleven months after index surgery, he underwent implant removal and articulating antimicrobial cement spacer application in both knees (Fig. 1a) and was referred to our institute. He presented with difficulty in mobilization due to displaced cement spacer in both knees, thick purulent discharge from left knee and copious sero-purulent discharge from right knee. Laboratory investigations revealed Erythrocyte Sedimentation Rate (ESR) of 22 mm and a C-reactive protein (CRP) at 27 mg/L. All antibacterials were stopped, tissue samples excised from sinus edge and discharge from both knees sent for microbiological analysis.
Bacteriology and mycology laboratory reports were inconclusive. In the mycobacteriology laboratory, the Ziehl Neelsen stain and Gene-Xpert MTB/RIF from the material was negative. Some growth was observed on MacConkey agar on day 3. Colonies were confirmed as AFB and grew on Lowenstein Jensen's media with 5% NaCl. Nitrate reduction test was negative. MGIT automated liquid culture system (Becton Dickinson, NJ, USA) revealed the growth of the same phenotype. As per the growth pattern and biochemical properties the isolate was identified as Mycobacterium abscessus. The isolate was sequenced for 16S ribosomal gene and confirmed as M. abscessus, The sequence was submitted to Genbank and granted Accession No. MH720215. Drug susceptibility test was done by broth micro-dilution assay as per CLSI guidelines. The isolate was sensitive to amikacin, clarithromycin, linezolid and rifampin but resistant to imipenem.
The patient was started on rifabutin 300 mg, clarithromycin 1000 mg and injection amikacin 500 mg daily. Baseline audiometry, renal function tests, ECG and liver function tests were within normal limits. Serial QTc monitoring, renal function, electrolytes and liver enzymes were closely monitored. After 3 weeks of antibacterial, thorough debridement of right knee with sinus excision, and distal femoral canal curettage followed by arthrodesis using Ilizarov ring fixator was done. After two weeks, the left knee was debrided and left with antimicrobial impregnated cement spacer in-situ. After another 8 weeks of antibacterials, the left knee was re-implanted with revision knee prosthesis and the patient was mobilized with full weight bearing on both knees. The intraoperative tissue samples on both knees revealed negative culture for mycobacteria.
Post-intervention, there was no fresh discharge from both knee joints (Fig. 1b). PET scan at end of four months revealed no metabolic uptake. Amikacin was replaced with oral levofloxacin due to bilateral sensory-neural hearing loss for higher frequencies after 6 months. By end of 7 months, his wounds were clean and dry, ESR, CRP were within normal limits. Ilizarov ring fixator was removed and knee brace used as the X-ray showed signs of trabeculae across the distal femur and proximal tibia. Currently the patient is on one-and-half year follow-up and is antimicrobial free for last four months. He is mobile without braces, is able to bear weight on both his legs for last two months, and a normal for age renal and liver functions. His latest X-rays showed bony ankylosis of right knee with stable revision knee arthroplasty implants in situ in his left knee (Fig. 1c).