An Inflammatory Myopathy in the Dutch Kooiker Dog

Abstract

The Dutch Kooiker dog (het Nederlandse Kooikerhondje) is one of nine Dutch dog breeds. As of 1960, a number of heritable diseases have been noted in this breed. One is an inflammatory myopathy that emerged in 1972, with numbers of affected dogs gradually increasing during the last few decades. The objective of this paper is to describe clinical signs, laboratory results, electromyography and histopathology of the muscle biopsies of the affected dogs. Method: Both retrospectively as well as prospectively affected Kooiker dogs were identified and categorized using a Tiered level of Confidence. Results: In total, 160 Kooiker dogs-40 Tier I, 33 Tier II and 87 Tier III-were included. Clinical signs were (1) locomotory problems, such as inability to walk long distances, difficulty getting up, stiff gait, walking on eggshells; (2) dysphagia signs such as drooling, difficulty eating and/or drinking; or (3) combinations of locomotory and dysphagia signs. CK activities were elevated in all except for one dog. Histopathology revealed a predominant lymphohistiocytic myositis with a usually low and variable number of eosinophils, neutrophils and plasma cells. It is concluded that, within this breed, a most likely heritable inflammatory myopathy occurs. Further studies are needed to classify this inflammatory myopathy, discuss its treatment, and unravel the genetic cause of this disease to eradicate it from this population.

Keywords: Kooiker dog; autoimmune disease; dog; dysphagia; myopathy; myositis.

Figure 1

Number of Kooiker dogs identified in the last 5 decades.

Figure 2

Histology of a skeletal muscle of a Kooiker dog with an extensive mainly lymphohistiocytic myositis with only a limited number of recognizable muscle fibers (arrows). H&E stain, obj. 20×.

Figure 3

Skeletal muscle of a Kooiker dog with numerous neutrophils (arrows), next to a lymphohistiocytic infiltrate. H&E stain, obj. 40×.

Figure 4

Skeletal muscle of a Kooiker dog with an extensive lymphohistiocytic myositis. Several muscle fibers are hypereosinophilic with loss of cross striation and are sometimes fragmented (arrows). H&E stain, obj. 10×.

Figure 5

Skeletal muscle of a Kooiker dog with a marked variation in the severity of the myositis (severe upper left side and minimal lower right side) between different muscle fascicles. H&E stain, obj. 10×.

Figure 6

Skeletal muscle of a Kooiker dog with a lymphohistiocytic myositis. Immunohistochemistry reveals numerous mononuclear cells with prominent membranous and mild cytoplasmic immunoreactivity consistent with macrophages (brown cells). IBA1 immunohistochemistry, obj. 20×.

Figure 7

Skeletal muscle of a Kooiker dog with a lymphohistiocytic myositis. Immunohistochemistry reveals numerous mononuclear cells with prominent membranous and mild cytoplasmic immunoreactivity consistent with T-lymphocytes (lightly colored brown cells). CD3 immunohistochemistry, obj. 20×.

Figure 8

Immune cell phenotyping. Myofiber invasion (frames) is mostly driven by T cells (A) and macrophages (C), but not by B cells (B). All cells are scattered throughout the inflamed interstitial tissue (asterisks). (A–C): diaminobenzidine, counterstained with hematoxylin-eosin.