Nematode-associated Intramural Alimentary Nodules in Pumas are Histologically Similar to Gastrointestinal Eosinophilic Sclerosing Fibroplasia of Domestic Cats

Summary Intramural alimentary nodules in the gastric pylorus and proximal duodenum are a common finding in free-ranging pumas ( Puma concolor ) in North America, and are often associated with the presence of an indwelling nematode (most commonly Cylicospirura spp.). This study compares the histological, histochemical and immunohistochemical appearance of three proximal gastrointestinal nodules in pumas with four cases of eosinophilic sclerosing fibroplasia in domestic cats. Histologically, the pattern of inflammation and repair was strikingly similar, consisting of lamillated anastomosing trabeculae of dense sclerotic collagen with interspersed inflammatory cells and reactive fibroblasts. The stromal trabeculae were histologically reminiscent of osteoid and were uniformly positive for collagenous protein by Masson's trichrome stain and negative for mineralized osteoid deposits with Von Kossa's stain. Trabecular cells expressed osteonectin, but not osteocalcin immunohistochemically. Collectively, these findings are most consistent with a stroma comprised of dense collagenous trabeculae that resembles, but is distinct, from osteoid. Both the puma and domestic cat lesions demonstrated an eosinophilic inflammatory component; however, eosinophils were present in small numbers in the puma nodules relative to the nodules in domestic cats. These entities likely represent a unique and stereotypic gastrointestinal repair response of felids, given their similar histological, histochemical and immunohistochemical profiles.