Introduction

• Cause: multiple causes, including chronic antigenic stimulation, neoplasia, infectious diseases.
• Signs: in the skin papules, nodules and plaques are found. If respiratory signs are present, they include epistaxis, and difficulty breathing.
• Diagnosis: by cytology and histopathologic examination of biopsy samples.
• Treatment: no effective treatment for horses with multiple lesions.
• Prognosis: varies on extent and severity of the lesion.

Pathogenesis

Etiology

• In the systemic form it is proposed that chronic infection and antigenic stimulation    →   deposition of amyloid fibrils (AA amyloid) by macrophages. In this case the fibrils are produced from serum ±-globulin.
• In the organ specific form it is proposed that allergens may   →   deposition of amyloid fibrils (AL amyloid). These fibrils are formed by monoclonal immunoglobulin light chains.

Predisposing factors

• Chronic infection/antigenic/allergenic stimulation.

Specific

• Systemic form is associated with chronic infections, eg tuberculosis, coccidioides, strangles   Strangles (Streptococcus equi infection)  .
• In the organ specific form either allergies or neoplasia, eg malignant histiolymphocytic lymphosarcomas      Skin: neoplasia - lymphosarcoma    Lymphoproliferative disorders   plasmacytoma.

Pathophysiology

• See etiology.

Timecourse

• Variable from few weeks to months.

Epidemiology

• Rare disease.

Diagnosis

Treatment

Outcomes