Lymphocytic thyroiditis with an oncocytic alteration in a laboratory beagle

Abstract

Histopathological, immunohistochemical, and ultrastructural characteristics of lymphocytic thyroiditis in an untreated four-year-old male beagle were described. Histopathologically, the thyroid glands were composed of two distinct cell types: round to oval cells with eosinophilic granular cytoplasm (Type A), which is consistent with the features of oncocytic oxyphils, and larger round cells with amphophilic or pale cytoplasm (Type B). These cell types extensively and diffusely infiltrated with a mixture of lymphocytes and plasma cells, destroying the follicular structure. Immunohistochemistry revealed that Type A cells were positive for thyroglobulin and cytochrome C, and that Type B cells were positive for calcitonin, synaptophysin, and cytochrome C. These results indicate that Type A and B cells stem from follicular and C cells, respectively. Ultrastructural investigation showed that microfollicles and microvilli were evident in the cytoplasm and along the luminal surface of Type A cells. Thus, the lymphocytic thyroiditis observed in the beagle exhibited a morphology similar to that of Hashimoto thyroiditis in humans, particularly in view of an oncocytic alteration of follicular cells.

Keywords: Hashimoto disease; dog disease; oncocytic alteration; oxyphil cells; thyroiditis.

Fig. 1.

Histopathological features of the thyroid glands in beagles. (A) The thyroid was replaced by eosinophilic cellular clusters, accompanied by lymphoplasmacytic infiltration. Few normal choroidal-filled follicles. HE. (B) Eosinophilic cellular clusters and lymphoplasma infiltration. HE. (C) CD3-positive T cells. Immunostaining for CD3. (D) CD20-positive B cells. Immunostaining for CD20. (E) Abundant collagen bundles crisscrossing the thyroid gland. MT. (F) The remaining follicles are lined with cuboidal and hypertrophic epithelial cells. HE. (G) Colloids in the remaining follicles. PAS reaction. (H) Two cell types, Type A (arrowheads) and Type B (arrows). HE. Bars=1,000 μm (A), 250 μm (B, C, D, E), 100 μm (H) and 50 μm (F, G).

Fig. 2.

Histopathological features of clusters of the two cell types in beagle dogs. Type A (A–D) and Type B (E–H) were stained with HE, PAS, MT, and PAM in order from the left. Type A cells had vacuoles (Fig. 4. A, arrowheads), and the vacuoles were positive for PAS staining (Fig.4. B, arrowheads). Inset in photograph A: Eosinophilic granular cells with hyperchromatic nuclei. Bars=50 μm.

Fig. 3.

Immunohistochemistry of thyroglobulin (A–D), calcitonin (E–H), synaptophysin (I–L), cytochrome C (M–P), and Ki-67 (Q–T) for Type A, Type B, remaining follicles, and a normal thyroid (a 1-year-old male beagle), respectively. Bars=50 μm.

Fig. 4.

Immunohistochemistry of thyroglobulin for Type A synaptophysin for Type B. Type A accounted for approximately 60% of lesions in all clusters. Bars=2 mm.

Fig. 5.

Electron microscopy. (A) Intracytoplasmic microfollicles (MF) and microvilli (arrowheads) along the luminal surface in Type A. (B) No colloid droplets were reabsorbed in the epithelial cells of the remaining follicle (RF). The number of secretory granules in Type B cells was consistent with that in type C cells. The inset shows a high-magnification view of the secretory granules. Bars=2 μm (A), 10 μm (B).