What is your diagnosis? Nasal lesion in a horse.

This study presents the case of a 6-year-old male castrated Quarter Horse with a suspected diagnosis of nasal amyloidosis, a rare disease characterised by local deposition of amyloid within the nasal passages, which was evidenced through various physical examinations, magnetic resonance imaging, and biopsy studies.

Case Presentation

• The Quarter Horse was being evaluated for its bilateral epistaxis (nose bleeding) and lesions in the nasal septum.
• The horse presented with bilateral serosanguineous nasal discharge and ulceration of the rostral nasal passages.
• MRI scans of the nasal passages revealed lesions localised to the mucosa, specifically the rostral nasal septum and floor of the nasal cavity, devoid of cartilage or bone involvement.
• Biopsies of the affected mucosa from both nasal passages were taken and processed for cytology (study of cells) and histopathologic evaluation (study of changes in tissues causing diseases).

Interpretation

• The cytological study found many plasma cells and moderate numbers of macrophages which often contained granular to fibrillar, gray to brightly eosinophilic material.
• The histopathologic study showed that the submucosa, mucosal epithelium, and glands were infiltrated by plasma cells. Eosinophilic to amphophilic material and associated granulomatous inflammation were also found.
• The amyloid substance found extra-cellularly and within macrophages stained red-orange with Congo red, and emitted bright green birefringence under polarised light – characteristics typical of amyloid proteins. However, testing for immunoreactivity for j or k light chains typically present in amyloid remained inconclusive.

Discussion

• Nasal amyloidosis, an uncommon horse disease, is characterised by amyloid deposition within the nasal passages. The cause remains unknown.
• Clinical signs of the disease can vary from epistaxis, nasal discharge to dyspnea (difficulty in breathing) depending on the severity of the lesions.
• The horse’s symptoms were typical for nasal amyloidosis. However, the histological findings were unique.
• While amyloidosis generally refers to tissue deposition of amyloid, it could be seen in various diseases in which different amyloid proteins are produced and deposited either locally or systemically.
• There is a possibility that plasma cells were responsible for the amyloid deposition in this particular case. The amyloid in equine nasal amyloidosis lesions is usually of light chain type (AL amyloid). Unfortunately, the tests to confirm this were inconclusive in this case.