Chronic lymphocytic thyroiditis in a cynomolgus macaque (Macaca fascicularis)

Area of Science:

• Veterinary Pathology
• Toxicology
• Endocrinology

Background:

• Chronic lymphocytic thyroiditis (CLT) is an autoimmune condition affecting the thyroid gland.
• Pituitary gland adaptations can occur secondary to thyroid dysfunction.
• Cynomolgus macaques are frequently used in preclinical toxicology studies.

Purpose of the Study:

• To report a spontaneous case of chronic lymphocytic thyroiditis in a cynomolgus macaque.
• To characterize the pathological features of the observed thyroiditis and associated pituitary changes.
• To discuss the implications for interpreting findings in toxicology studies.

Main Methods:

• Necropsy and histopathological examination of thyroid and pituitary glands.
• Immunohistochemistry (IHC) for B-cell (CD20) and T-cell (CD3) markers.
• IHC for thyroid stimulating hormone (TSH) in pituitary cells.

Main Results:

• Multifocal follicular lymphoid infiltrates with germinal centers, thyroid acinar atrophy, and pituitary cell hyperplasia/hypertrophy were observed.
• Lymphoid infiltrates were confirmed as B-cells (CD20+) and T-cells (CD3+).
• Pituitary cells showed positivity for TSH, indicating a compensatory response.

Conclusions:

• The observed pathology in the cynomolgus macaque resembles human Hashimoto's disease.
• Spontaneous CLT with compensatory pituitary changes can occur in cynomolgus macaques.
• Findings emphasize the need for caution when interpreting thyroid and pituitary alterations in toxicology studies.