Case Report: The Use of In Vivo Confocal Microscopy for Diagnosis and Monitoring in a Rare Case of Ancaliia algerae Microsporidial Keratitis in New South Wales, Australia

ABSTRACT.

We describe the successful management of Ancaliia Algerae microsporidial keratitis in an immunosuppressed 54-year-old woman with refractory linear IgA disease. The case highlights the challenges in diagnosis and management of this infection in immunocompromised individuals and emphasizes the usefulness of in vivo confocal microscopy as a novel, noninvasive tool to aid in the diagnosis and monitoring of microsporidial keratitis. We also discuss the possible mode of acquisition of this rare infection.

INTRODUCTION

Microsporidia are ubiquitous obligate intracellular organisms that produce environmentally resistant spores.¹ There are approximately 220 described microsporidian genera, and 17 species have been implicated as human pathogens.¹ The microsporidian Ancaliia algerae (former genera Brachiola and Nosema) is an emerging human pathogen, with cases reported from Australia, New Zealand, and North America.^2–7 We describe a case of A. Algerae microspordiosis manifesting as ocular keratitis in an immunocompromised individual in which in vivo confocal microscopy (IVCM), a novel noninvasive diagnostic method, was used for diagnosis and monitoring.

CASE PRESENTATION

A 54-year-old female presented to the emergency department with 3 days of redness, epiphora, and pain affecting the left eye. This was on a background of refractory linear IgA disease treated with prednisone 5 to 20 mg once daily and mycophenolate sodium 720 mg twice daily. The case patient reported several months of generalized myalgias and proximal weakness. There was no history of contact lens use. The case patient lived in Sydney, Australia, within a 5-km radius of three golf courses, but there was no clear exposure to these untreated water sources. On examination, there was normal visual acuity bilaterally. The left eye showed a raised fleshy subconjunctival lesion adjacent to the plica semiluminaris and occasional tarsal conjunctival follicles in the upper and lower eyelids (Figure 1). There was also diffuse punctate epitheliopathy, but the cornea was otherwise clear. There was no muscle tenderness or weakness. Serum creatine kinase (CK) level was normal (71 unit/L). The CD4+ count was 76 cells/µL (normal range: 421–1,410).

Figure 1.

Image of left eye at presentation—raised, fleshy, erythematous lesion with possible extension into the plica semiluminaris.

The differential diagnoses included infective keratoconjunctivitis, immune-related conjunctivitis due to linear IgA disease, and conjunctival lymphoma. Treatment with topical prednisolone acetate 1% lead to a deterioration in the eye with worsening epitheliopathy. The prednisone was ceased, and topical chloramphenicol 1% and valaciclovir 1,000 mg orally three times daily were commenced as empirical cover for herpes virus disease.

There was further deterioration of the left eye with reduced visual acuity of 6/60 and fine stellate keratic endothelial precipitates with mild anterior chamber inflammation. The corneal stroma was edematous with prominent folds in the Descemet membrane. The right eye was also inflamed with similar epithelial signs that had preceded in the left eye but without a reduction in vision. Although empiric ofloxacin 0.3% topically every 1 hour to both eyes was commenced, swabs of the right and left corneas and a scrapings of the left cornea showed no cells or organisms on microscopy and no bacterial growth on culture.

Microsporidial polymerase chain reaction (PCR) of corneal swabs/scrapings and partial epitheliectomy tissue was negative for Encephalitozoon spp., Enterocytozoon spp., and Vittaforma corneae. In vivo confocal microscopy performed with a white halogen globe at 500× level of magnification showed small intracellular hyper-reflective bodies, indicative of microsporidial spores (Figure 2).⁸ Amplification of additional microsporidial targets were requested and Ancaliia algerae was identified by PCR product sequence analysis using primer pairs NALGf2/NALGR1 and NAGf/NAG178r.²

Figure 2.

In vivo confocal microscopy images (magnification 500×). (A) Left cornea (deep)—there is a central large macrophage/keratocyte surrounded by small intracellular (solid arrows) and extracellular (hollow arrows) hyperreflective bodies that represent microsporidial spores. (B) Right cornea—small zone of subepithelial white cell recruitment with central keratocyte filled with microsporidial spores (arrows).

Topical voriconazole 1% four times daily to both eyes and albendazole 400 mg orally two times daily were commenced. A muscle biopsy was not performed to determine the presence of A. algerae myositis in the absence of signs of myopathy, a normal serum CK, and initiation of systemic therapy with albendazole. Initially, immunosuppression was reduced for the control of linear IgA disease with the cessation of mycophenolate and the commencement of low prednisone therapy (10 mg daily) in combination with plasma exchange.

The patient’s keratitis showed near complete resolution after 8 weeks of treatment with symptomatic recovery, and VA was 6/6 bilaterally. This was accompanied by a marked reduction in the number of organisms in the interstitial tissue and fewer cells with inclusions evident on IVCM, and a reconstitution of the CD4 population to > 250 cells/µL.

However, progression of the linear IgA disease required recommencement of mycophenolate therapy. At 6 months, the patient remained asymptomatic with 6/6 visual acuity bilaterally with no organisms evident on IVCM. Topical voriconoazole was ceased, and albenzadole was continued for 12 months while the patient was maintained on mycophenolate therapy. The patient was monitored for adverse effects including liver dysfunction and tolerated the therapy.

DISCUSSION

Ancaliia algerae infection primarily causes myositis; however, corneal, cardiac, cutaneous, and disseminated infection have also been described in case reports.^2–7 Most patients at diagnosis were immunosuppressed from treatment of rheumatoid arthritis or hematological malignancy or after solid organ transplantation.^3–7 Interestingly, the two previous cases of A. algerae corneal infection have been reported in immunocompetent individuals.^9,10

Insects, including mosquitos, are hosts for A. algerae, but the mechanism of acquiring systemic human infection is unclear.^4,11 Microsporidial keratitis may occur through direct inoculation through contact with contaminated water.^2,4,12 Earlier reports propose exposure to A. algerae from untreated water through bathing or showering¹⁰ or living in close proximity to woodlands or bodies of untreated water, such as those found on a golf course.^2,3 The proximities of these golf courses to the residence ranged from < 100 m to 1 km.^2,3 In addition, five of the eight previously documented patients with A. algerae infection resided in NSW, Australia.^2–4 In the case study, however, the closest body of water was on a golf course 2 km from the patient’s residence. This study is the first reported case of A. algerae keratitis in a patient with known immunodeficiency. It is plausible that the threshold for A. algerae infection in this study patient including the distance from untreated water was decreased due to immunosuppression.

Microsporidial keratitis can clinically mimic other causes of keratitis, such as herpes simplex stromal keratitis.¹² Furthermore, microsporidia are fastidious organisms and can be difficult to culture.¹⁰ Light and electron microscopy can be performed on biopsies of affected tissue to facilitate the diagnosis of microsporidiosis.¹² However, due to the limited material retrieved from corneal scraping, there is significant risk of false-negative results.⁸ In vivo confocal microscopy was a key imaging tool used for both diagnosis and monitoring in this case. IVCM uses a 670-nm wavelength diode laser, the Heidelberg Retina Tomograph, to obtain in vivo imaging of the anterior segment.¹² In microsporidial keratitis, IVCM can be used to identify intracellular and extracellular hyper-reflective oval spores.⁸ The sensitivity and specificity of IVCM in detecting microsporidia has not been reported.¹² In this case, IVCM allowed successful identification of both intracellular and extracellular microsporidial organisms involving the stroma and keratocytes (Figure 2). Further identification of the microsporidia could then be performed with PCR, and specific treatment can be commenced. Our case supports the use of IVCM as a first-line, noninvasive screening tool for suspected microsporidial keratitis, minimizing the initial need for tissue biopsy.⁸ Malhotra et al. (2017) described consistent IVCM findings of hyper-reflective, pinpoint oval intracellular bodies within rosette-like clusters of epithelial cells in eight patients who were confirmed to have microsporidial keratitis on corneal scraping. They posited that these features may be used as a screening tool when microsporidial keratitis was suspected, precluding the need for corneal scrapings in many patients. Our case supports this and demonstrates the utility of IVCM as a noninvasive method for monitoring the response to therapy.⁸

There are multiple species of microsporidia proven to cause ocular infection. Early identification with PCR is key, having important implications for treatment and prognosis.^12–14 In this case, the standard PCR panel for microsporidial species was negative, and subsequent molecular testing for A. algerae was requested based on highly suggestive IVCM findings and existing epidemiological data from the region.² When microsporidial infection is considered as a potential cause for undifferentiated keratitis, it is important that PCR testing is not limited to only a few microsporidial targets.

Albendazole has been successfully used to treat systemic A. algerae infection, with the addition of fumagillin in a refractory case.^4,5 Various regimens have been used to treat microsporidial corneal infections, including systemic albendazole and topical treatments with fumagillin, voriconazole, and propamidine isethionate 0.1%.^8,15–17 In our case, the combination of topical voriconazole and systemic albendazole enabled not only treatment of acute disease in addition to the marked reduction of immunosuppressive therapy, but it was also effective in suppressing reactivation of disease during the recommencement of immunosuppression.

Our case highlights the importance of considering A. algerae infection as a differential diagnosis in patients presenting with keratitis in immunocompromised individuals, particularly those living in potentially endemic areas or who have had exposure to untreated water. In vivo confocal microscopy is a useful means for noninvasive visualization of microsporidia at diagnosis and for monitoring response to a therapeutic strategy comprising topical and systemic treatment. Microsporidial PCR allows for confirmation of the diagnosis and testing for a wide range of PCR targets is crucial if the suspicion of microsporidial keratitis is high.