JPC SYSTEMIC PATHOLOGY
Signalment (JPC #1380452): Adult male Siamese cat
HISTORY: This cat presented with a small circular raised nodule on its head. Similar, occasionally ulcerated nodules later developed on the head, ears, nose and forelimbs. The animal was euthanized and this section taken from the ear at the time of necropsy.
HISTOPATHOLOGIC DESCRIPTION: Haired skin, pinna: Infiltrating the dermis, separating and effacing adnexa, and elevating a mildly hyperplastic epidermis are multiple coalescing nodules composed of numerous macrophages and neutrophils with fewer perivascular and periadnexal lymphocytes and plasma cells. There are numerous intrahistiocytic and extracellular 4-10 um diameter, round to oval, lightly eosinophilic yeast that are occasionally surrounded by a clear halo. The epidermis is focally ulcerated and mildly hyperplastic, with acanthosis and spongiosis. There is rare neutrophilic exocytosis.
PAS: There are numerous intrahistiocytic and extracellular pleomorphic (round, oval and occasional cigar-shaped) PAS-positive yeast.
MORPHOLOGIC DIAGNOSIS: Haired skin, pinna: Dermatitis, pyogranulomatous, nodular, multifocal, moderate, with numerous intrahistiocytic and extracellular PAS-positive yeast, etiology consistent with Sporothrix schenckii, Siamese, feline.
ETIOLOGIC DIAGNOSIS: Aural cutaneous sporotrichosis
CAUSE: Sporothrix schenckii
- An opportunistic, dimorphic, saprophytic fungus found in moist organic debris, sphagnum moss and hay
- Grows as a mycelium at environmental temperature and a yeast in tissue (at temperatures greater than 35 degrees Celsius)
- Disease is uncommon, seen most frequently in cats, horses, dogs and humans
- Especially roaming intact male cats and hunting dogs
- Disease occurs more frequently in temperate and tropical zones
- Three clinical forms:
- Primary cutaneous form
- Most common form reported in dogs and cats
- Lesions confined to point of entry of organism
- This form may result from high degree of host immunity which prevents spread
- Cutaneous-lymphatic form
- Most common form reported in horses
- Lesions confined to skin and subcutis but follow lymphatics
- Extracutaneous / Disseminated form
- Sequela to cutaneous-lymphatic form or inhalation
- Rare in dogs, but most frequently reported in cats; occasionally seen with corticosteroid use in dogs
- Primary cutaneous form
- Infection acquired by wound contamination or inoculation by puncture wounds caused by thorns (especially rose and barberry), wood splinters, contaminated claws, cat bite or pruned fir trees
- Direct transmission from cats to people (zoonotic potential)
- Typically limited to the skin/subcutaneous tissue but occasionally disseminated
- schenckii organisms are commonly cultured from the blood in cats with both widespread and localized cutaneous lesions
- Some authors hypothesize that the severity of feline sprotrichosis is due to immunosuppression from co-infection with FeLV/FIV, but studies have not been able to show an association
- Pulmonary infections are rare and result from inhalation of the organism
TYPICAL CLINICAL FINDINGS:
- Cats with disseminated form are febrile, depressed and anorexic.
- Respiratory signs are the most frequent extracutaneous clinical findings
TYPICAL GROSS FINDINGS:
- Primary cutaneous: Lesions usually involve head, pinnae and trunk in dogs and the head, distal limbs and tail base in cats; single or multiple raised, nodules or plaques (1-5 cm diameter) confined to point of entry of organism, often with ulceration, red-brown purulent exudate and crusting
- Grooming behavior of cats may result in autoinoculation and spread to distant sites
- Cutaneous-lymphatic: Lesions usually involve proximal forelimbs, chest and thighs (without evidence of regional lymph node involvement); multiple nodules, arranged in lines form along the course of the lymphatics which are often thick and corded; often ulcerated with purulent discharge; lesions may cavitate exposing extensive areas of muscle and bone
- Extracutaneous/Disseminated: Usually occurs without identification of immunosuppression; may involve a single extracutaneous tissue or multiple internal organs; develops as sequela of cutaneous-lymphatic form or inhalation of conidia
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Diffuse and/or nodular pyogranulomatous dermatitis and panniculitis—epidermis is acanthotic or ulcerated with variable fibrosis
- The yeast are pleomorphic, round, oval or cigar-shaped; single or budding cells; 2-6 microns in diameter and 2-10 microns in length; refractile cell wall- shrinkage artifact may cause yeast to appear encapsulated
- Organisms are numerous in lesions in cats and rare in dogs and horses
- Found extracellularly in the lesion’s purulent core or within cytoplasm of macrophages, multinucleate giant cells and neutrophils
- Splendore-Hoeppli material may surround the fungus forming asteroid bodies
ADDITIONAL DIAGNOSTIC TESTS:
- Yeast are gram-positive and PAS, GMS positive, serial sections may be needed
- Cytology of exudate with PAS or GMS stain
- Fungal culture
- Indirect immunoperoxidase or direct fluorescent antibody with schenckii antiserum
- Polyclonal anti-Mycobacterium bovis (BCG) stain may help identify organisms
- A rapid (24 hours) molecular detection method has recently been described and has been used successfully to identify the organism directly in biopsy specimens from an infected cat
Solitary (or multiple) ulcerated and fistulated dermal lesions in cats and dogs:
- Opportunistic or systemic fungal infections (cryptococcosis, histoplasmosis, blastomycosis)
- Bacterial abscesses/severe bacterial pyoderma
- Foreign body reactions
- Sterile granuloma and pyogranuloma syndrome
- Feline leprosy (Mycobacterium lepraemurium)
Cutaneous equine lymphangitis with draining tracts:
- Epizootic lymphangitis/pseudoglanders (Histoplasma capsulatum var. farciminosum): Ulcerative, nodular pyogranulomatous lymphangitis usually of hind limbs and neck
- Glanders/Farcy (Burkholderia mallei): Neutrophilic to pyogranulomatous ulcerative lymphangitis of the head and neck
- Melioidosis (Burkholderia pseudomallei): Wide host range; often causes an ascending lymphangitis of the distal extremities
- Ulcerative lymphangitis (Corynebacterium pseudotuberculosis): Ascending neutrophilic to granulomatous ulcerative lymphangitis of the lower limbs (especially fetlock) with intracellular and extracellular diphtheroid bacteria
- Equine strangles (Streptococcus equi ssp. equi): Regional lymph node abscesses most severely affecting the mandibular and retropharyngeal lymph nodes that often rupture and discharge pus
- Histoplasma capsulatum: 2-4 um diameter yeast within macrophages with single narrow-based budding (hourglass appearance)
- Cryptococcus neoformans: 2-20 um diameter yeast, with thick mucin positive 2 um thick capsule; forms single or multiple narrow-based buds; stains well with mucicarmine
- Blastomyces dermatitidis: 8-25 um diameter, round, multinucleated yeast with thick walls (double contoured), single broad-based buds
- Cutaneous leishmaniasis: Chronic ulcerative dermatitis with 2 um intrahistiocytic protozoal amastigotes with vesiculate nucleus and kinetoplast
- Reported in cattle, mules, donkeys, goats, swine, rats, mice, hamsters, domestic fowl, camels, dolphins, armadillos and chimpanzees
- The organism is difficult to find in species other than the cat
- Occupational hazard for people working closely with vegetation or soil; risk factors include rose gardening, topiary production, hay baling and Christmas tree farming
- Crothers SL, White SD, Ihrke PJ, Affolter VK. Sporotrichosis: a retrospective evaluation of 23 cases seen in northern California (1987-2007). Vet Dermatol. 2009;20(4):249-259.
- Gross TL, Ihrke PJ, Walder EJ, Affolter, VK eds. Skin Diseases of the Dog and Cat- Clinical and Histopathologic Diagnosis. 2nd ed. Ames, IA: Blackwell Science Ltd.; 2005: 298-301.
- Hargis AM, Ginn PE. The integument. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 5th ed. St. Louis, MO: Mosby Elsevier; 2007: 1040.
- Jang SS, Walker RL. Fungal and algal diseases. In: Greene CE, ed. Infectious Diseases of the Dog and Cat. 4th ed. St. Louis, MO: Elsevier Saunders; 2012: 645-650.
- Mauldin EA, Peters-Kennedy J. Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier; 2016: 655-657.
- Miranda LH, Quintella LP, Santos IB, et al. Comparative histopathological study of sporotrichosis and American tegumentary leishmaniasis in dogs from Rio de Janeiro. J Comp Pathol. 2010;143(1):1-7.
- Schubach TM, Schubach A, Okamoto T, et al. Evaluation of an epidemic of sporotrichosis in cats: 347 cases (1998-2001). J Am Vet Med Assoc. 2004:224(10):1623-1629.
- Scott DW, Miller WH Jr, eds. Equine Dermatology. St. Louis, MO: Elsevier Science; 2003: 296-298.