Punch biopsies of an ulcerated plaque in the nasal mucosa of a male-castrated, 12-year-old, Quarter horse were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) in 10% buffered formalin for histopathologic examination. History noted that the ulcerated plaque was a squamous cell carcinoma or an infection.
Histologically, there was no evidence of neoplasia or infection. The microscopic lesions consisted of severe hyperplasia of the nasal mucosa. The submucosa exhibited fibrosis, areas of mild hemorrhage, moderate to large numbers of hemosiderin-laden macrophages, moderate infiltration of lymphocytes and plasma cells, and focal moderate mineralization of the connective tissue and the wall of small arteries. Numerous islands of homogeneous, hyaline, eosinophilic material were present between submucosal stromal fibroblasts, blood vessels, and glands. The eosinophilic material stained orange-red with Congo red special stain and exhibited green birefringence under polarized light. Based on the microscopic findings, a diagnosis of nasal amyloidosis was established.
Amyloidosis is a relatively rare disease in equines and can be systemic or localized. The systemic form is generally the reactive or secondary type resulting from deposition of amyloid apoprotein (AA type) secondary to chronic inflammatory conditions. The primary or localized form, referred as AL amyloidosis is rarely systemic and involves the deposition of insoluble monoclonal immunoglobulin (Ig) light (L) chains or L-chain fragments secondary to abnormal amyloid production by plasma cells. Both systemic and localized AL amyloidosis may occur in horses
Localized nasal amyloidosis is an infrequent clinical entity in the horse, seldom associated with other underlying disease. Amyloid deposits usually form single or confluent nodules of variable size in one or both nostrils. The lesions may extend to the septum, the floor of the nasal cavity and to the nasopharyngeal area and conjunctiva.
Some of the clinical signs reported include nasal obstruction causing dyspnea and epiphora. Affected horses may show stertor and exercise intolerance. Epistaxis occurs in some cases as a consequence of increased fragility of the nasal mucosa and blood vessels. The cause of nasal amyloidosis in the horse is unknown, but a case of equine nasal amyloidosis secondary to multiple myeloma has been reported.
The differential clinical diagnoses for nasal amyloidosis include squamous cell carcinoma and other nasal neoplasms, fungal granulomas of the nasal septum (sinonasal cryptococcal granuloma), progressive ethmoid hematoma and glanders.
Localized amyloid plaques can be removed surgically to provide symptomatic relief, but in some horses the amyloid plaques reoccur. Localized radiotherapy may decrease the size of the amyloid plaques, but there are no effective practical treatments for extensive lesions.
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REFERENCES
Oluk MA, Murphy J. Nasopharyngeal amyloidosis: An unusual cause of epistasis. J. Laryngology Otology. 124:209-212, 2010.
Russel LA, Navas de Solis C, Whitfield-Cargile CM, Deveau MA, Buchanan BR, Gilmour LJ. Imaging findings associated with nasopharyngeal amyloidosis in an Arabian stallion. Equine Vet. Educ. 2018.
Shaw DP, Gunson, DE, Evans LH. Nasal amyloidosis in four horses. Vet. Pathol. 24:183-185, 1987.