Rhinosporidiosis

Background

Rhinosporidiosis is a chronic granulomatous infection of the mucous membranes that usually manifests as vascular friable polyps that arise from the nasal mucosa or external structures of the eye.

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Granulomatous mass involving structures of the eye. Image used with permission from doctorfungus.org.

Initially described by Seeber in 1900 in an individual from Argentina,^[1] rhinosporidiosis is endemic in India, Sri Lanka, South America, and Africa.^{[2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]} Cases from the United States and Southeast Asia, as well as scattered occurrences throughout the world, have also been reported. Most cases of rhinosporidiosis occur in persons from or residing in the Indian subcontinent or Sri Lanka. In addition to humans, rhinosporidiosis has been noted in cats, cattle, dogs, ducks, goats, horses, mules, parrots, and swan.^[15]

The etiologic agent, Rhinosporidium seeberi, has never been successfully propagated in vitro. Initially thought to be a parasite, for more than 50 years R seeberi had been considered to be a water mold.^[16] Molecular biological techniques have more recently demonstrated this organism to be an aquatic protistan parasite, and it has been placed into a new class, the Mesomycetozoea, along with organisms that cause similar infections in amphibians and fish.^{[17, 18, 19]} This reclassification is not without controversy, as other researchers have presented data that R seeberi is a cyanobacterium, further demonstrating the difficulties that arise when working with pathogens that cannot be maintained in the laboratory setting.^{[20, 21]} Other molecular work has demonstrated evidence that R seeberi may have host-specific strains (eg, human vs dog vs swan).^[22]

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Pathophysiology

Rhinosporidiosis is an infection that is typically limited to the mucosal epithelium. Infection usually results from a local traumatic inoculation with the organism. The disease progresses with the local replication of R seeberi and associated hyperplastic growth of host tissue and a localized immune response.

Infection of the nose and nasopharynx is observed in 70% of persons with rhinosporidiosis; infection of the palpebral conjunctivae or associated structures (including the lacrimal apparatus) is observed in 15%.^[23]

Other structures of the mouth, upper airway, and eye may be sites of disease. Disease of the skin, ear, larynx, trachea, bronchi, genitals, and rectum has also been described.^[24] Genital rhinosporidiosis has been described in the vagina, penile urethra or meatus, and scrotum.^[25] Dissemination with cutaneous and multisite disease is also reported, but this is much less common. Isolated cases of dissemination involving deep organs have been rarely reported.^{[26, 27]}

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Epidemiology

Frequency

United States

Rhinosporidiosis cases in the United States are rare but are more common in Texas and the Southeast.

International

Rhinosporidiosis usually affects persons in or from southern India and Sri Lanka. Cases have been reported worldwide, with an increased incidence in South America and Africa.

Mortality/Morbidity

Rhinosporidiosis can cause prolonged painless disease with limited morbidity. Disease of up to 30 years' duration has been reported. Secondary bacterial infection can cause morbidity. Death has been reported in only the few rare reports of disseminated rhinosporidiosis.

Race

Rhinosporidiosis has no known racial predilection.

Sex

Men are affected more commonly than women, with a male-to-female ratio of 4:1.

Age

Rhinosporidiosis most commonly occurs in children and in individuals aged 15-40 years.

Risk Factors

Rhinosporidiosis has been associated with rural residence, occupation in farming or agriculture, and bathing in ponds or rivers.^{[28, 29, 30]}

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Prognosis

The prognosis of rhinosporidiosis is excellent, except with dissemination, as described above (see Mortality/Morbidity).

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Patient Education

Patients with rhinosporidiosis should be advised that recurrence is possible. They should be instructed to return for further evaluation if symptoms recur or new symptoms arise.

Cases of dissemination or more extensive disease have been associated with a prior history of both treated and untreated nasal disease. Accordingly, ensure that patients are instructed to (1) be vigilant for a recurrence of symptoms or new lesions and (2) promptly consult with their physician if these are noted.

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History

Nasal rhinosporidiosis may present with unilateral nasal obstruction or epistaxis. Other symptoms may include local pruritus, coryza with sneezing, rhinorrhea, and postnasal discharge (drip) with cough. Patients often report a sensation that a foreign body is present in their nasal canal.

Eye involvement is initially asymptomatic. Increased tearing may be reported as the disease progresses. Photophobia, redness, and secondary infection may occur.

Skin lesions begin as papillomas that gradually become verrucous.

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Physical

Soft polyps may develop on the nose or eye. These polyps are pink to deep red, are sessile or pedunculated, and are often described as strawberrylike in appearance. Because the polyps of rhinosporidiosis are vascular and friable, they bleed easily upon manipulation. This appearance results from sporangia, which are visible as gray or yellow spots in the vascular polypoid masses.

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Causes

The etiologic agent of rhinosporidiosis, R seeberi, has traditionally been considered a fungus. Recent 18S ribosomal ribonucleic acid (rRNA) gene analysis has placed R seeberi into a novel group of aquatic parasites of the class Mesomycetozoea, some of which cause similar diseases in amphibians and fish.^{[17, 18, 19]}

Most persons with rhinosporidiosis have had bathing or working exposure to stagnant water.^{[6, 31]}

No immune deficiency has been associated with infection.

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Complications

Complications of rhinosporidiosis include extremely rare, life-threatening dissemination, local secondary bacterial infection, and recurrence.

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Laboratory Studies

Direct observation

Rhinosporidiosis is diagnosed by identifying the typical structures of R seeberi directly on microscopic examination. This includes examination of smears of macerated tissue or histology of prepared biopsy sample sections.

The organism can be observed with typical fungal stains (eg, Gomori methenamine silver [GMS], periodic acid-Schiff [PAS]), as well as with standard hematoxylin and eosin (H&E) staining.

Smears can also be observed with potassium hydroxide (KOH) preparation.

Serologic testing

Serologic testing (immunoblot (dot – enzyme-linked immunosorbent assay [ELISA]) identification of antirhinosporidial antibody) has been developed and used for epidemiologic studies in endemic areas, but this testing is not available for or routinely used in patient diagnosis.^{[32, 31]}

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Imaging Studies

Recent evaluation of the use of computed tomography (CT) imaging to delineate the site and extent of disease has been published.^[33] Moderate-to-intense enhancement by CT was noted in the majority of lesions in the 16 people included in that study.

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Histologic Findings

In 1923, Ashworth described in detail the life cycle of the organism in tissue.^[16] This cycle begins with a round endospore that is 6-10 µm in diameter. The endospore grows to become a thick-walled sporangium of 100-350 µm in diameter that contains up to several thousand endospores. These structures are similar to the smaller endospores (2-5 µm in diameter) and spherules (30-60 µm in diameter) of Coccidioides immitis.

The sporangia of R seeberi are observed under the normal epithelium. They are associated with immune cells, including neutrophils, lymphocytes, plasma cells, and multinucleated giant cells, often in scattered granuloma. Papillomatous hyperplasia and hypervascularity are also common. See the images below.

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Sporangia of Rhinosporidium seeberi within nasal polyp (periodic acid-Schiff [PAS] stain). Image used with permission from doctorfungus.org.

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Sporangia of Rhinosporidium seeberi in polyp (Gomori methenamine silver [GMS]) stain. Image used with permission from doctorfungus.org.

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Medical Care

Rhinosporidiosis is treated with surgical excision because, generally, medical treatment has not been proven effective. However, multiple reports of successful treatment of individuals with long courses of dapsone have been published.^{[34, 35]} This drug may be useful in individuals with multisite rhinosporidiosis.

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Surgical Care

Local surgical excision is the treatment of choice for rhinosporidiosis. Recurrence has been reported with simple excision. Wide excision with electrocoagulation of the lesional base has been promoted to decrease recurrences.

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