BI20 A fatal case of disseminated cutaneous Mycobacterium chelonae infection in an immunocompromised patient
Authors: Kerkemeyer Karolina , Vyas Aparna , Walker Stephen , Rickaby William 
Published: June 2024

Abstract
An 82-year-old multimorbid male patient on haemodialysis for the complications of end-stage cardiorenal syndrome and long-term oral prednisolone for bullous pemphigoid was referred to our department for a suspicious pigmented lesion. At initial review, he incidentally reported a 6-week history of tender raised lesions. There was no associated cough, headache, loss of appetite, unintentional weight loss or fever. Skin examination revealed a 1.2 × 0.9-cm atypical darkly pigmented nodule on the left anterior shin. Erythematous-to-violaceous tender dermal papules and nodules were located on bilateral cheeks and anterior thighs. There was no palpable lymphadenopathy. Differential diagnoses included cutaneous melanoma metastases or infection. Excisional biopsy of the pigmented nodule confirmed invasive superficial spreading melanoma with a Breslow thickness of 1.8 mm. Punch biopsy from a representative lesion demonstrated features suspicious for an infectious aetiology showing dermal suppurative granulomatous inflammation with associated necrosis and neutrophil polymorphs with abundant karyorrhectic debris. Stains for microorganisms (Ziehl–Neelsen, Grocott, Gram, Wade–Fite, diastase periodic acid–Schiff) were negative. Repeat biopsy was advised. The patient was subsequently admitted to hospital with worsening pulmonary and peripheral oedema. An erythematous oedematous plaque with discharging yellow exudate overlying the proximal interphalangeal joint of the fourth digit on the right hand was noted. White cell count and C-reactive protein were elevated to 19.8 (normal 3–10) × 109 L−1 and 80.5 (normal 0–5) mg L−1, respectively. Peripheral blood cultures were negative. X-ray highlighted patchy radiolucency with cortical destruction of the middle phalanx and distal aspect of the proximal phalanx of the right ring finger, and intravenous flucloxacillin was commenced for suspected Staphylococcus aureus osteomyelitis. Further lesional punch biopsies were taken. Despite standard antibacterial treatment, he experienced increasing confusion and oxygen requirement. A family decision was made to withdraw active therapy and transition to end-of-life care. The patient unfortunately died the following day. Subsequent histopathological assessment demonstrated a diffuse suppurative and histiocytic inflammatory cell infiltrate that extended from the superficial dermis to the subcutis. Wade–Fite staining identified filamentous structures suggestive of atypical mycobacteria. Culture ultimately grew Mycobacterium chelonae. M. chelonae is a rapidly growing, nontuberculous mycobacteria. It is ubiquitous in both natural and human-made environments and can be acquired via direct inoculation (e.g. following contaminated healthcare and aesthetic procedures). M. chelonae most commonly causes chronic skin, bone and soft tissue infection. Disseminated infection is primarily seen in immunocompromised patients. Diagnosis is challenging owing to the heterogeneous clinical presentation, necessitating collaboration between dermatologists, histopathologists and microbiologists. This case underscores the importance of maintaining strong clinical suspicion for atypical infections, particularly in immunocompromised cohorts.