A 4-year-old Exotic breed cat, living in Hong Kong was presented with a subcutaneous mass located at the abdomen, that was clinically suspected to correspond to a mammary gland neoplasm. The mass was not ulcerated. During processing, two masses were detected in the surgical specimen one measuring 2×1.5x1cm and another 1x1x0.6cm. The histologic evaluation revealed a nodular to diffuse pyogranulomatous dermatitis, extending from the superficial dermis deep into the subcutis with intralesional fungal hyphae. Fungi was pleomorphic and refractile, with variable sized clear bulbous and thick-walled dilations, resembling spores, distributed free and embedded in a Splendore-Hoeppli reaction or occasionally inside the cytoplasm of macrophages.
Tissue from the skin with coalescing granulomatous inflammation surrounding Splendore-Hoeppli material containing bulbous and thick-walled fungal hyphae.
- What is this skin disease?
- What fungi is associated with this condition?
- What cat breeds are affected by this condition?
Written by Dr. Ana R. Resendes
Click for the Answer
- This skin disease is known as dermatophytic pseudomycetoma and is a rare to uncommon in both cats and dogs. The disease presents as solitary to multiple cutaneous and subcutaneous nodules most often located at the dorsal thorax.
- In cats this condition is associated with Microsporum canis and in dogs with both Canis and Trichophyton mentagrophytes.
- In cats, the syndrome is seen almost exclusively in Persian and to a lesser extent in Himalayan cats. This marked breed predilection suggests that a genetically preprogrammed, selective immunodeficiency may play a role in the development of dermatophytic pseudomycetoma in this breed.
- Dermatophytic pseudomycetoma is an unusual clinical presentation of dermatophytosis in which dermatophilic fungi form hyphae in dermal and subcutaneous tissue. The disease is rare to uncommon in both dogs and cats.
- The disease manifests as nonpainful, nonpruritic, firm dermal or subcutaneous nodules that may ulcerate and form draining tracts. Lesions are most frequently found on the trunk, flanks, or tail. Concurrent superficial dermatophytosis is common. Lymphadenopathy may be present. These nodules need to be differentiated from neoplasia, foreign body reactions, and other nodular infectious to non-infectious skin conditions, specially other fungi. Histopathology is diagnostic because the morphologic features of the fungi are distinctive. Fungal culture confirms Microscoprum canis or Trichophyton mentagrophytes
- It is suspected that traumatic implantation of organisms into the dermis is responsible for the formation of the pseudomycetoma. This traumatic implantation of organisms could result from fights or mating behaviour. Positive dermatophyte cultures from normal-appearing areas distant from the dermatophytic pseudomycetoma indicate that affected cats may previously have been inapparent carriers. Inapparent carriage of Microsporum canis is common in Persian and Himalayan cats.
- Lesions should be surgically excised, if possible, and systemic antifungal therapy should be administered. The prognosis is fair to poor, with drug resistance and relapses common. Affected animals are potentially contagious and can cause superficial dermatophytosis in other animals and in humans.
- Small animal dermatology: A Color Atlas and Therapeutic Guide 4th Edition (2017). Editor(s): Keith A. Hnilica and Adam P. Patterson. Chapter 4: Fungal Diseases.
- Skin diseases of the dog and cat: Clinical and Histopathologic Diagnosis, 2nd Edition (2005). Editor(s): Thelma Lee Gross; Peter J. Ihrke, Emily J. Walder, Verena K. Affolter. Chapter 12. Infectious Nodular and Diffuse Granulomatous and Pyogranulomatous Diseases of the Dermis.