Sir,

The genus Nocardia encompasses saprophytic, aerobic, Gram-positive, nonmotile, weakly acid-fast, and branching filamentous bacteria. Ocular manifestations of Nocardia infection vary. Isolated scleritis due to Nocardia species are rare.1 Scleritis usually spreads from corneal infection involving the limbus. The identification of the organism to species level is important as antimicrobial susceptibility patterns may vary widely between Nocardia species. Reported predisposing factors for scleritis due to Nocardia are trauma, cataract surgery, exposed scleral buckle, and contact lens wear.2, 3, 4, 5, 6 We are unaware of a previous report on Nocardia nova infection in the Eye.

Case report

A 40-year-old woman presented with a 10-week history of excruciating pain and redness in the left eye. She was using topical steroid and oral nonsteroidal anti-inflammatory drugs (NSAIDs) for the previous 4 weeks. There was a history of mud splashed into her face 1 week before symptom onset, although she did not feel any splash into the eyes. She had a history of hepatitis C and past intravenous drug use, but denied injecting intravenous drugs for the past 10 years. Her only regular medication was methadone. At initial examination, her visual acuity in both eyes was 6/6. Her right eye examination revealed no abnormality.

Slit-lamp examination of the left eye showed a single focal superonasal elevated (size 6 × 6 mm in diameter and 2 mm elevation) subconjunctival-congested nodule (Figure 1a). It was firm. The cornea was clear and anterior chamber was quiet. The posterior segment was normal. Oral prednisolone (60 mg) was started, with immediate resolution of pain. However, the nodule persisted and 3 weeks later the apex of the nodule became yellow. The appearance and the lack of response to therapy suggested an infective aetiology. Therefore, biopsy was planned and performed via a fornix-based flap. Nocardia species was recognised by its characteristic Gram-positive filamentous appearance on Gram stain and modified acid-fast stain. Topical and oral steroids were quickly tapered and ceased. The patient was commenced on 5% amikacin sulphate drops 2 hourly and oral trimethoprim/sulphamethoxazole (TMP-SMX 160/800 mg b.i.d.). After 5 days, she developed generalised pruritus, redness, and skin dysaesthesia, which were attributed to an adverse drug reaction to TMP-SMX. Systemic medication was changed to amoxicillin-clavulanate (800/125 mg b.i.d. orally). Subconjunctival injection of amikacin sulphate (100 mg) was administered and repeated 2 days later. Generalised moderate conjunctival injection followed the biopsy and worsened after the subconjunctival amikacin injection.

Figure 1
figure 1

(a) Clinical photograph of superonasal scleral nodule before biopsy. (b) Clinical photograph after resolution of nodule showing scleral thinning.

Full size image

N. nova was identified by sequence analysis of the 16S rRNA gene, an established technique for this organism.7 Once the organism was identified as N. nova, the patient was changed to oral amoxicillin (500 mg t.i.d.) and clarithromycin (500 mg b.i.d.). The organism was sensitive to erythromycin, TMP-SMX, sulphamethoxazole, clarithromycin, and amikacin. It was resistant to amoxicillin-clavulanate, tobramycin, and ciprofloxacin with intermediate sensitivity to minocycline. After 6 weeks, the nodule resolved, but moderate generalised conjunctival injection persisted. Topical fluorometholone acetate 0.1% q.i.d. was reinstituted and topical amikacin was continued for 3 months, as were oral amoxicillin and clarithromycin. Scleral thinning persists after resolution of the nodule (Figure 1b). She has developed a 1 × 1 mm posterior subcapsular cataract and the final visual acuity is 6/6 unaided in her left eye.

Systemic examination and investigation, including a magnetic resonance image of her brain revealed no other foci of nocardiosis, although there is a 1 mm hyperintensity in the pons thought to be artefact.

Comment

Infections due to Nocardia are uncommon in immunocompetent patients. Most infections are due to the Nocardia asteroides group, which includes the N. asteroides complex, N. farcinia and N. nova, which are differentiated by their characteristic antibiotic susceptibility patterns.8 The various ocular manifestations of Nocardia infection are chronic conjunctivitis, keratoconjunctivitis, corneal ulcer, chronic orbital infection, chorioretinitis, endophthalmitis, scleritis, dacryoadenitis, and canaliculitis.9 We are not aware of any previous cases of ocular infection with N. nova, but it is possible that previous cases where the N. asteroides group has been implicated may have included N. nova as the group share similar biochemical characteristics.

Trauma related to agricultural work is the usual predisposing factor to nocardia keratitis and scleritis.10 However, it is an unusual presentation of nocardia scleritis to present as a nodule without any necrosis or discharge. Corticosteroids are known to worsen the infection, probably by stabilising the lysosomal granules and inhibiting release of lysosomal enzymes, thereby preventing the destruction of phagocytosed intracellular nocardial organisms. It is possible that initial therapy of systemic and topical prednisolone might have aggravated the condition in our case. This report also emphasises the role of biopsy for diagnosis in this unusual manifestation.

Previous reports have listed various topical and systemic antibiotics in the management of Nocardia infection; most Nocardia species are susceptible to topical amikacin and systemic TMP-SMX. N. nova is reported to have an unusual susceptibility pattern due to the presence of a beta-lactamase induced by clavulanic acid.8 However, the patient responded to topical and subconjunctival amikacin before the introduction of systemic amoxicillin and clarithromycin.

This report of N. nova ocular infection reinforces the role of biopsy for diagnosis of this unusual organism. This and previous reports suggest that scleral nocardiosis should be treated with topical amikacin, with adjuvant systemic antibiotics dictated by species identification and susceptibility.