The diagnosis and treatment of rapidly growing non-tuberculous mycobacterial keratitis

Abstract

To study the clinical features, diagnosis and treatment of non-tuberculous mycobacterial keratitis (NTMK). It was retrospective case series study. Twelve eyes in 12 patients with NTMK following corneal foreign body trauma in 2007 were studied retrospectively including the case histories, clinical findings, laboratory examinations, diagnosis, treatment and prognosis. The main laboratory examination included corneal scrapings by culturing, polymerase chain reaction (PCR) and transmission electron microscopy (TEM), corneal lesions by histopathologic examinations and TEM. The patients received local and systemic antibiotics therapy, lesion cleaning followed by cauterization with tincture of iodine (5%) and (or) keratoplasty. All cases had a history of corneal trauma, there was corneal metallic foreign body removal at one hospital in 11 cases, corneal reed trauma in 1 case. The characteristic signs involved grayish-blue crystalloid keratopathy, multifocal infiltrates, satellites, radical form changes in the Descemet's membrane. The results of laboratory examinations of the scrapings of the cornea infection were as follows: all cultures (12/12) were positive for rapidly growing mycobacteria, and isolates from 5 patients were all diagnosed as mycobacterium chelonae subspecies abscess; acid-fast staining revealed positive bacilli in all the 4 patients; seven of 8 patients were positive for bacterium by PCR. Transmission electron microscopy in all the 3 specimens showed many slender rod-shaped or short coarse-shaped bacteria which were phagocytized by monocytes, and some necrotic tissue. Infections in 10 eyes were resolved by combined treatment regimen including a combination of antimicrobial agents (amikacin, rifampin, gatifloxacin, ciprofloxacin, azithromycin and/or ofloxacin, etc.) and local lesion cleaning followed by cauterization with 5% tincture of iodine within 2-5 months; two cases resolved by keratoplasty which poorly responded to antibiotic therapy for 6 months. NTMK is a rare, recalcitrant opportunistic infection which can occur in an epidemic fashion following corneal foreign body trauma. The diagnosis of NTMK is difficult, and may easily be misdiagnosed as fungal keratitis. Acid-fast staining, TEM, especially bacterial culture can help to obtain definitive diagnosis. NTMK has a long response period to medical management. The majority of patients can be cured by local and systemic antibiotics therapy, and the recalcitrant infections could be resolved by keratoplasty.