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Non-tuberculous mycobacteria (NTM) or atypical mycobacterial keratitis is an uncommon condition causing indolent corneal ulceration. The infection mimics herpetic, mycotic, and Nocardia keratitis and diagnosis requires a high index of suspicion. We report two cases of NTM infection where the presenting sign was that of crystalline keratopathy. Both cases were diagnosed by microbial culture and successfully treated.
A 44 year old white female contact lens wearer presented with a 3 week history of an inflamed eye with a 1.5 mm diameter area of corneal stromal infiltration. Vision was 6/6 in each eye. She was being treated with antivirals and later unsuccessfully with antibacterials and steroids. Three active stromal crystalline infiltrates appeared in the mid-stroma 3 weeks later (fig 1). Culture from a corneal biopsy revealed Mycobacterium chelonei.
The keratitis responded to topical amikacin and amphotericin B, which was started on the suspicion of fungal keratitis, before microbial culture results were available. The keratitis resolved over a 4 week period and vision settled at 6/9.
An 80 year old white woman with pseudophakic bullous keratopathy had a penetrating keratoplasty and was given systemic tacrolimus. Three months postoperatively she presented with endothelial dusting and a 1 mm mid-stromal abscess with a crystalline appearance (fig 2). A corneal scrape revealed acid fast bacilli for which she was commenced on topical ciprofloxacin and amikacin 2.5% but was slow to respond. Culture confirmed Mycobaterium chelonei resistant to amikacin. Topical moxifloxacin was added and oral clarithromycin commenced. Three months later, the ulcer healed with a clear graft but the vision did not improve (counting fingers) on account of pre-existing macular oedema.
Non-tuberculous mycobacteria cause indolent corneal ulceration resembling herpes virus, fungal, or Nocardia keratitis. The variable clinical presentations and poor susceptibility to conventional antibacterials usually results in a delay in diagnosis.1–3 The two common types of NTM causing keratitis are M chelonei and M fortutium. The clinical features of NTM include pseudodendritic epithelial defects, subepithelial white fluffy infiltrates with crystalline satellite lesions and ulcers with an overhanging necrotic edge and a grey sloughed base.1 Keratic precipitates and endothelial deposits may appear. Early diagnosis is difficult and absence of organisms in smears and cultures does not exclude the diagnosis of NTM. Repeat scrapes or a corneal biopsy should be considered in all indolent corneal ulcers.
Amikacin has been the drug of choice in Nocardia and atypical mycobacterial infection.1,2 However, approximately 60% of patients will not respond to topical amikacin, as with our second case, and use of combination therapy with ciprofloxacin, gatifloxacin, moxifloxacin, and clarithromycin is recommended.4–7 Penetrating keratoplasty is performed when stromal infiltration is extensive4 but immunosuppression may predispose to recurrent infection. Both our patients were treated successfully. The first patient had a good visual outcome but the second had poor vision due to pre-existing pathology. Successful treatment requires disease awareness, deferring the use of steroids when no organism has been isolated and use of effective antibiotics.