Mycobacterium of an unknown strain causing a primary tumoral process of the orbital roof

PURPOSE. To report an unidentified species of atypical Mycobacterium as the causative agent of a primary orbital roof infection. METHOD. Review of a case from the King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia. RESULTS. The patient had a negative history for eye trauma. Computed tomography (CT) of the brain and right orbit confirmed the presence of soft tissue swelling and erosive changes in the orbital roof bone, with intact globe and external ocular muscles. Biopsy of the lesion showed non-caseating, granulomatous osteomyelitis. Various stains of the sample were negative. Since our institution could not identify the causative organism, a biopsy sample was sent to Bioscientia Laboratory in Germany; the culture grew an atypical Mycobacterium of unknown species. Their sensitivity study showed the organism to be resistant to pyrazinamide, isoniazide and streptomycin, but sensitive to rifampicin, ethambutol, and prothionamide. Systemic checkup and investigation ruled out any other systemic involvement. CONCLUSION. A new species of atypical Mycobacterium was recovered from a primary orbital infection. The infection responded to combined antituberculous therapy.