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Nontuberculous Mycobacteria Keratitis


Key Concepts

  • Nontuberculous mycobacterial (NTM) keratitis commonly occurs after trauma or refractive surgery, and can masquerade as fungal, herpetic, or amoebic keratitis, often delaying the diagnosis.

  • NTM keratitis has been most commonly reported following laser in situ keratomileusis (LASIK). Mycobacterium chelonae and Mycobacterium fortuitum are the most commonly identified species.

  • Diagnosis of NTM keratitis is difficult and often causes a delay in initiation of treatment. NTM are acid-fast aerobic bacilli and laboratory diagnosis can be made with either the Ziehl−Neelson acid-fast stain, inspissated egg media (Lowenstein−Jensen media), or broth media (Middlebrook 7H9 and 7H12).

  • In post-LASIK cases, lifting the flap for cultures and irrigation with antibiotics will aid diagnosis and potentially improve resolution of infection. Flap amputation should be considered.

  • An aggressive and prolonged antibiotic treatment regimen for NTM keratitis should include a fourth-generation fluoroquinolone, amikacin, and clarithromycin. Linezolid is a potential newer agent for cases resistant to other antibiotics.

  • Steroids are not recommended in the treatment of NTM keratitis.

  • Surgical intervention in the form of corneal transplantation may be required to help clear an active and nonresponsive infection or may be needed for visual rehabilitation due to scarring from the infection.

Overview

Nontuberculous or “atypical” mycobacterial keratitis continues to be a diagnostic and therapeutic challenge. In 1965, Turner and Stinson reported the first case of keratitis secondary to Mycobacterium fortuitum following the removal of a corneal foreign body. Since their initial report, numerous individual case reports and small case series have been published. Nontuberculous mycobacteria (NTM) have emerged as major pathogens causing severe postoperative microbial keratitis following laser in situ keratomileusis (LASIK). Recently, a case of bilateral NTM keratitis after small-incision lenticule extraction (SMILE) was reported in the literature.

NTM keratitis is characterized by a delayed onset of symptoms of 1–14 weeks following corneal trauma or surgery, followed by an even further delay in diagnosis. A case of post-LASIK keratitis showed a latent period of 4 years. Medical treatment can be quite difficult and often requires prolonged and intensive topical and systemic therapy. Surgical intervention including lamellar keratectomy, penetrating keratoplasty (PK), and in LASIK-associated cases, flap removal, is frequently needed.

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