Immune Mediated Polymyositis In The Dutch Kooiker Dog

Within the Dutch Kooiker dog (het Nederlandse Kooikerhondje), one of nine
Dutch dog breeds, we have described earlier, an inflammatory myopathy that presents
itself with clinical signs of primarily dysphagia, locomotion problems, or a
combination of both. The first cases emerged in 1972 and up to now over 170 affected
Kooiker dogs, originating from various countries, have been identified. The
outcome of this disease was in most cases fatal as affected dogs died withing 2
years after diagnosis. We further investigated and characterized the histopathological
changes in muscle tissue and immunophenotyped the inflammatory infiltrates.
FFPE-fixed muscle biopsies from 39 Kooiker dogs were included and evaluated
histopathologically according to a tailored classification scheme for skeletal
muscle inflammation. Immunophenotyping revealed primarily lymphohistiocytic
infiltrates, with CD3+ T-cells being the predominant inflammatory cell type, accompanied
by CD8+ cytotoxic T-cells. The concurrent expression of MHC-II class
molecules on myofibers suggests their involvement in initiating and maintaining
inflammation. Additionally, CD20+ B-cells were identified, though in lower numbers
compared to T-cells, and IBA-1 positive macrophages were frequently seen.
These findings suggest a breed-specific subtype of polymyositis in Kooiker dogs,
akin to other breeds. The study sheds light on the immune response activation,
combining adaptive and innate mechanisms, contributing to our understanding of
polymyositis in this breed.