JPC SYSTEMIC PATHOLOGY
Signalment (N27784F): Unknown age and gender Doberman pinscher
HISTORY: Presented with multiple non-pruritic, draining fluctuant nodules and fistulous tracts on the face, trunk and extremities along with exercise intolerance and ocular discharge. The right eye had a grade 2/4 flare, rubeosis iridis and conjunctival injection. The pupil would not dilate and the fundus could not be assessed. The left eye had a detached retina.
HISTOPATHOLOGIC DESCRIPTION: Eye: Diffusely, the retina is separated from the retinal pigmented epithelium by a copious exudate composed of numerous viable and degenerate neutrophils, macrophages, rare multinucleated giant cells (foreign body type), myriad viable and degenerate yeast, many of which are within macrophages as well as extracellular and abundant eosinophilic homogenous to fibrillar and lacy material (fibrin and edema). The yeast are 12-18 um diameter with a 2-3 um thick wall, a centrally located eosinophilic or basophilic granular nucleus and occasional broad base budding. Diffusely, the overlying detached retina is convoluted and expanded by fibrin, edema and congestion. Multifocally along the choroid, retinal pigmented epithelial cells are hypertrophic. The choroid, ciliary body and iridial stroma are edematous, congested and are infiltrated by numerous plasma cells, macrophages and fewer neutrophils and lymphocytes. The posterior and anterior chambers contain abundant fibrin. Multifocally in the cornea there are numerous small blood vessels lined by plump endothelial cells (vascularization), separated by loosely arranged collagenous stroma with plump fibroblasts and rare lymphocytes, macrophages and neutrophils.
- Eye: Endophthalmitis, pyogranulomatous, diffuse, severe with retinal detachment and numerous budding yeasts, etiology consistent with Blastomyces dermatitidis, Doberman pinscher, canine.
- Eye, cornea: Keratitis, chronic-active, multifocal, mild with vascularization.
ETIOLOGIC DIAGNOSIS: Mycotic ophthalmitis
CAUSE: Blastomyces dermatitidis
CONDITION: North American blastomycosis
- Systemic mycotic disease caused by a dimorphic soil saprophyte
- Endemic areas are centered around wet and swampy areas to include Mississippi, Missouri, Ohio River valleys and mid-Atlantic states; also found in Europe, Asia, the Middle East and Africa
- Most frequently reported cause of intraocular mycosis in dogs; mainly young outdoor dogs; rare in cats
- Ocular manifestations reported in up to 50% of dogs with systemic blastomycosis
Fungal conidia are inhaled > lung > hematogenous or lymphatic spread to various body systems (including the eye)
TYPICAL CLINICAL FINDINGS:
- Clinical signs reflect the involved tissue; respiratory symptoms from granulomatous pneumonia are most common
- Eye: Anterior uveitis, panophthalmitis, chorioretinitis, retinal detachment, secondary glaucoma and optic neuritis
- Blastomycosis has been associated with pulmonary embolism in a dog
TYPICAL GROSS FINDINGS:
Pyogranulomatous or granulomatous endophthalmitis, granulomatous optic neuritis and exudative retinal separation
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Diffuse pyogranulomatous or granulomatous endophthalmitis with chorioretinitis, hyalitis, exudative retinal separation, cataract(s) and often granulomatous optic neuritis
- Anterior uveitis usually less pronounced than choroiditis
- Lens capsule rupture
- Round or oval 5-25 um diameter yeasts with thick, sharply defined, refractile cell walls
- Yeast are usually found in the choroid, but may rarely be found in the anterior segment and retina
- Single broad-base budding
ADDITIONAL DIAGNOSTIC TESTS:
- Special stains: Gomori methenamine silver (GMS); Periodic acid Schiff (PAS); Gridley fungal stain (GF)
- Vitreous aspirates often contain organisms
- Urine Blastomyces antigen testing: High sensitivity for active disease at the time of diagnosis and during treatment; moderate sensitivity, but high specificity for clinical relapse
Mycotic ocular infections:
- Cryptococcus neoformans: Predominantly within retina, choroid, and optic nerve; often no inflammation; yeast are 5-20 um with narrow based budding and thin cells well and a thick capsule (halo)
- Coccidioides immitis: Rare; generally a more destructive lesion than other mycoses; often suppurative panophthalmitis with pyogranulomatous reaction around fungal spherules; endosporulation; larger than Blastomyces dermatitidis (30-100 um)
- Histoplasma capsulatum: Lymphoplasmacytic and histiocytic choroiditis or panuveitis, retinal separation, optic neuritis; small yeasts (2-4 um) within macrophages
- Prototheca : Algae causing marked inflammation in the choroid, retina and subretinal space; ovoid or angular organism (8-20 um)
- Generalized disease with Aspergillus and Candida sp. may involve the eyes in immunosuppressed animals
- Cat: Rare cause of ocular mycosis
- Horse: Disseminated blastomycosis
- California sea lion: Disseminated blastomycosis
- Non-human primate: Disseminated form in a rhesus monkey
- Alpaca: Disseminated blastomycosis (genetic group 2)
- American black bear: Disseminated blastomycosis
- Rat: Probable infection in a young rat
- Arceneaux KA, Taboada J, Hosgood G. Blastomycosis in dogs: 115 cases (1980-1995). J Am Vet Med Assoc. 1998;213(5):658-664.
- Chang SC, Hsuan SL, Lin CC, et al. Probable Blastomyces dermatitidis infection in a young rat. Vet Pathol. 2013;50(2):343-346.
- Connolly SL, Frank C, Thompson CA, et al. Dual infection with Pythium insidiosum and Blastomyces dermatitidis in a dog. Vet Clin Pathol. 2012;41(3):419-423.
- Dykstra JA, Rogers LL, Mansfield SA, Wuenschmann A. Fatal disseminated blastomycosis in a free-ranging American black bear (Ursus americanus). J Vet Diagn Invest. 2012;24(6):1125-1128.
- Foy DS, Trepanier LA, Kirsch EJ, Wheat LJ. Serum and urine Blastomyces antigen concentrations as markers of clinical remission in dogs treated for systemic blastomycosis. J Vet Intern Med. 2014;28(2):305-310.
- Hendrix DVH, Rohrbach BW, Bochsler PN, English RV. Comparison of histologic lesions of endophthalmitis induced by Blastomyces dermatitidis in untreated and treated dogs: 36 cases (1986-2001). J Am Vet Med Assoc. 2004;224(8):1317-1322.
- Houseright RA, Webb JL, Claus KN. Pathology in Practice. Blastomycosis in an indoor-only cat. J Am Vet Med Assoc. 2015 Aug 15;247(4):357-9.
- Huckabone SE, Gulland FM, Johnson SM, et al. Coccidioidomycosis and other systemic mycoses of marine mammals stranding along the central California, USA coast: 1998-2012. J Wildl Dis. 2015;51(2):295-308.
- Imai DM, McGreevey N, Anderson JL, Meece JK. Disseminated Blastomyces dermatitidis, genetic group 2, infection in an alpaca (Vicugna pacos). J Vet Diagn Invest. 2014;26(3):442-447.
- Labelle P. The eye. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Mosby; 2016:1301.
- McGuire NC, Vitsky A, Daly CM, Behr MJ. Pulmonary thromboembolism associated with Blastomyces dermatitidis in a dog. J Am Anim Hosp Assoc. 2002;38(5):425-430.
- Wilcock BP, Njaa BL. Special senses. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 6th ed. Vol 1. St. Louis, MO: Elsevier Inc; 2016:449-450.
- Wilson JH, Olson EJ, Haugen EW, Hunt LM, Johnson JL, Hayden DW. Systemic blastomycosis in a horse. J Vet Diagn Invest. 2006;18(6):615-619.
- Zwick LS, Briggs MB, Tunev SS, Lichtensteiger CA, Murnane RD. Disseminated blastomycosis in two California sea lions (Zalophus californianus). J Zoo Wildl Med. 2000;31(2):211-214.