A 68-year-old pseudophakic male with long-standing neurotrophic keratopathy secondary to HZO characterized by a non-healing corneal ulcer (Figure 1A), was referred with a recurrent Seidel-positive cornea of the left eye. Medical history was notable for chronic lymphocytic leukemia that was in remission after chemotherapy treatment (oral chlorambucil and combination fludarabine and cyclophosphamide). He developed herpes zoster with ocular involvement soon after completing the chemotherapy. Prior management of the neurotrophic cornea included topical lubricating; antibiotic and steroid drops; oral antivirals; injections of botulinum toxin for induction of ptosis; and amniotic membrane grafts (AMG). A corneal descemetocele had perforated 6 months prior and was managed with cyanoacrylate glue and a bandage contact lens.
Examination revealed cyanoacrylate glue on the central cornea with slow aqueous leakage, diffuse deep vascularization, an inferior stromal infiltrate, and a 1.5 mm layered hypopyon (Figure 1B). The glue was removed and re-applied after obtaining corneal scrapings, and topical vancomycin and tobramycin were administered empirically. Initial aerobic cultures were positive for micrococcus species, and acid-fast bacilli (AFB) stain was 3+ positive. Subsequent cultures grew M. abscessus. Topical amikacin and moxifloxacin and oral clarithromycin were started. Six weeks later, examination results remained unchanged.
A therapeutic penetrating keratoplasty (PK) with anterior chamber (AC) washout, AMG, subconjunctival bevacizumab injection, and permanent tarsorrhaphy were performed. AMG was used for its anti-inflammatory, anti-scarring, and wound healing properties on the ocular surface, and subconjunctival bevacizumab was used to help decrease corneal neovascularization. Initially, the patient recovered well but returned 20 days post-PK with painless 3+ white blood cells in the AC. B-scan ultrasonography showed dense retrolental opacity, concerning for endophthalmitis (Figure 2A). Vitreous tap and intravitreal injection of ceftazidime (2 mg/0.1 mL) and vancomycin (1 mg/0.1 mL) were performed with rapid improvement. Stains and cultures from the tap were negative. Histopathology from the host corneal button subsequently demonstrated AFB, and cultures were reported as M. abscessus (Figure 2B). The eye responded immediately to the administered antibiotics.
However, 9 months post-PK, the patient returned with minimal discomfort. There was no corneal infiltrate, but 4+ white blood cells in the AC, recurrent layered hypopyon (Figure 1C), mild anterior vitritis, and unaffected posterior vitreous were observed. A second vitreous tap and intravitreal injections of ceftazidime (2 mg/0.1 mL) and vancomycin (1 mg/0.1 mL) were administered based on prior responsiveness; however, this time, the patient did not improve. The tap revealed no organisms or cells, and cultures (aerobic, anaerobic, AFB, and fungal) and viral polymerase chain reaction (PCR) (to test for herpes simplex virus 1 and 2, and varicella zoster virus) were negative. Anterior and intermediate uveitis work-ups were performed (to test for tuberculosis, sarcoidosis, human leukocyte antigen B27, Lyme disease, and syphilis), and were negative.
Based on the recent negative work-up and failure to respond to therapy, as well as prior culture results, vitreous and AC biopsies, pars plana vitrectomy (PPV), AC washout, and injection of intravitreal antimicrobial and fungal agents (amikacin, 400 mug/0.1 mL; vancomycin, 1 mg/0.1 mL; and amphotericin B, 5 mug/0.1 mL), were performed. Antibiotic susceptibility testing was performed prior to this procedure on M. abscessus isolates grown from the prior host corneal button cultures, and showed high sensitivity to amikacin. Internal stains and cultures of the vitreous sample showed 2+ AFB positive staining, and culture results were reported as M. abscessus complex. Vitreous samples were also sent out to a validated laboratory (the University of Washington's, clinical microbiology laboratory; Seattle, WA, USA) for PCR and gene sequencing. PCR using primers targeting the 65 kDa heat shock protein (hsp65) gene and the beta subunit of ribonucleic acid polymerase (rpoB) gene was negative. However, sequencing of the 16S ribosomal ribonucleic acid (rRNA) gene was positive for M. abscessus/chelonae complex. Based upon the biochemical testing and gene sequencing results, the presumed cause of infection was M. abscessus.
After surgery, the eye again returned to a quiet state without evidence of infection or inflammation (Figure 1D), until the patient returned 3 months post-vitrectomy with painless clouding of vision in the left eye. Examination revealed presence of a layered hypopyon in the AC and 2+ inflammatory cells in the vitreous. Concern for recurrence of M. abscessus endophthalmitis prompted intravitreal injection of amikacin (400 mug/0.1 mL), but activity persisted despite an additional injection of amikacin (400 mug/0.1 mL) the following week. PPV and explantation of the posterior chamber intraocular lens and capsular bag with intravitreal injection of amikacin (400 mug/0.1mL), were then performed to eradicate mycobacteria that could be sequestered within the capsular bag. Pathologic examination of the capsular bag showed rare neutrophils, and Brown-Brenn and AFB stains were negative for bacteria and acid-fast organisms. However, AFB cultures of the vitreous cassette from the second vitrectomy were again reported as positive for M. abscessus, further substantiating the presumptive diagnosis of recurrent M. abscessus endophthalmitis. Since then, the eye has remained quiet without signs of infection for 11 months, and visual acuity is 20/70 with contact lens correction. The patient continues to be monitored closely by his ophthalmologists for recurrence.
Given the challenges encountered in identifying this organism, repeat PCR and gene sequencing were performed at the University of Rochester's clinical microbiology laboratory on culture growths from previously obtained vitreous samples from the two PPV procedures, for experimental purposes. 16S rRNA gene sequencing was first performed, which identified M. abscessus/chelonae complex. PCR as well as sequencing of the hsp65 gene was subsequently performed to differentiate between the two organisms. The result was the identification of M. chelonae. Since all prior biochemical testing had identified the organism as M. abscessus, and the initial send-out sequencing of the 16S rRNA gene had identified M. abscessus/chelonae complex, M. abscessus had been considered the most likely causative organism throughout the patient's clinical course. However, this discrepancy in identification upon repeat PCR and gene sequencing of the hsp65 gene was surprising. It is unlikely that both organisms co-existed in the patient's eye during his episodes of recurrent endophthalmitis. Given the greater reliability of PCR and sequencing of the hsp65 gene over traditional biochemical tests and culture techniques, we now believe that M. chelonae was likely the infectious agent all along and that the organism was initially misidentified on the basis of less accurate tests.