Nasal and ocular amyloidosis in a 15-year-old horse

Abstract

Localized nasal, conjunctival and corneal amyloidosis was diagnosed in a 15-year-old pony with nasal and conjunctival masses and severe dyspnoea. Multiple swellings had been evident in the nostrils for at least two years and had gradually increased in size before presentation due to dyspnoea and exercise intolerance. Surgical debulking of the masses was performed and histological examination revealed large amounts of extracellular, hyaline, eosinophilic, Congo red positive material in the lamina propria of the nasal mucosa. A tentative diagnosis of localized nasal amyloidosis was made. The treatment relieved the clinical signs, however, the nasal masses recurred and bilateral conjunctival, papillary masses developed. The horse was euthanized. Nodular nasal and papillary conjunctival masses consisting of rubbery, grey to yellow tissue were found at necropsy. At the limbus this tissue infiltrated and expanded the cornea. The masses consisted of amyloid and moderate infiltrates of T lymphocytes and B lymphocytes were present in the tissue. No predominance of either cell type was observed and no distinct neoplastic mass could be identified. Ultrastructural examination of the nasal mucosa and cornea confirmed the presence of abundant extracellular deposits of non-branching fibrils ranging from 9-11 nm in diameter consistent with amyloid. Immunohistochemistry of amyloid revealed no labelling for AA amyloid, and no peptides representing serum amyloid A (SAA) were detected by microscopic laser dissection and subsequent mass spectrometry. Peptides from immunoglobulin kappa-like light chains were detected and are suggestive of AL amyloidosis, however the results were inconclusive and a final identification of the amyloid protein could not be made.Nasal amyloidosis is a clinical entity of localized amyloid deposits in the horse. Localized amyloidosis involving the conjunctiva of the horse is previously described in only seven cases and the present case is the first case of combined, localized nasal and corneal amyloidosis in the horse. In several reported cases surgical excision has provided clinical improvement and return to normal levels of exercise, while medical treatment has had no effect. The present case however, shows that rapid recurrence and progression of nasal amyloidosis to involve ocular tissues can occur and lead to recurrent respiratory obstruction.