Veterinary Medicine - May 2008 - (Page 250) Histoplasmosis PEER-REVIEWED dogs, this form is characterized by a rapid onset of dyspnea and cyanosis. Dogs with chronic pulmonary histoplasmosis are presented for evaluation of a mild, chronic cough and a history of weight loss and inappetance.7 Coughing may be due to partial airway obstruction secondary to hilar lymphadenopathy.17 Most affected cats have disseminated disease, and, even with evidence of pulmonary involvement, they seldom cough.10,11,18 Other clinical signs of respiratory tract involvement include dyspnea and tachypnea.11 • Neurologic signs, including seizures and vertical nystagmus33 • Oral lesions, including gingival nodules and lingual erosions21,31 • Conjunctivitis, chorioretinitis, retinal detachment, or optic neuritis26,34 • Icterus9 • Pleural and peritoneal effusion7,23,35 CLINICAL PATHOLOGY AND DIAGNOSTIC IMAGING FINDINGS The results of routine diagnostic tests such as a complete blood count, a serum chemistry pro le, a urinalysis, and radiographic or ultrasonographic examinations may raise your suspicion of histoplasmosis. Feline disseminated histoplasmosis Clinical signs of feline disseminated histoplasmosis are often chronic and nonspeci c. Weight loss, pale mucous membranes, lethargy, pyrexia, anorexia, and dehydration were the predominant ndings in 12 cats with disseminated histoplasmosis. Five of the 12 cats were tachypneic with abnormal lung sounds.15 A review of 96 cases reported weakness, lethargy, emaciation, dehydration, and pyrexia as the most common signs.1 Respiratory signs such as dyspnea, tachypnea, and occasional coughing were noted in 39% of the cats.1 While sometimes reported to be uncommon, ocular involvement may occur in disseminated histoplasmosis more often than in other systemic mycoses in cats.1,36 In a review of 96 cats with histoplasmosis, 24% of the cats had ocular involvement including chorioretinitis, anterior uveitis, or retinal detachments.1 Granulomatous chorioretinitis occurs, possibly because of H. capsulatum in the choroid and retina.34,37 Additional ocular involvement may include retinal hemorrhage, optic neuritis, and fungal granulomas.15,38,39 About one-third of affected cats may have lymphadenopathy, splenomegaly, or hepatomegaly, occasionally accompanied by icterus.11 In contrast to dogs, primary intestinal histoplasmosis is unusual in cats; in one cat, this form of histoplasmosis caused vomiting and watery diarrhea with hematochezia.40 Cutaneous lesions, infrequently reported, are nodular or ulcerated and may exude serosanguineous uid.11,32,38,41-44 Neurologic signs also occur.45 Rare clinical ndings include nasal polyps and oral and lingual ulceration.10,11 Complete blood count The most common hematologic abnormality in dogs and cats with disseminated histoplasmosis is a normocytic, normochromic nonregenerative anemia.10,11,46 Anemia in dogs is usually mild to moderate; the packed cell volume (PCV) ranges from 20% to 37% (reference range = 35% to 57%47).8 In a report of 12 cats, anemia ranged from moderate (PCV = 20% to 25%) to severe (PCV < 20%) (reference range = 30% to 45%47).15 Causes of anemia may include intestinal blood loss, chronic in ammation, or bone marrow in ltration.8,11,30 Other hematologic abnormalities reported in dogs include monocytosis, neutrophilia, eosinopenia, and, less commonly, neutropenia, eosinophilia, basophilia, or a degenerative left shift.811,35,48,49 While infrequently observed, histoplasmosis is reported as a risk factor for neutropenia.48 Mild to severe thrombocytopenia may occur in as many as half of affected dogs.11 In a report of three dogs with histoplasmosis, platelet counts ranged from 5,000 to 81,000/mm3 (reference range = 211,000 to 621,000/mm3). Thrombocytopenia may be caused by increased platelet consumption or, possibly, sequestration in association with splenomegaly and hepatomegaly.46 A wide range of other hematologic abnormalities also occur in cats. Both neutropenia and neutrophilia have been reported,1,18,38,50 and pancytopenia was documented in one cat with toxic changes to the neutrophils.18 Thrombocytopenia may be observed in as many as one-third of affected cats.11 Chronically infected cats may not show any hematologic abnormalities.38 Canine disseminated histoplasmosis Acute disseminated histoplasmosis affects multiple organs, with a history of illness of only a few days’ duration in experimental animals.19 Gastrointestinal involvement was reported in 28 of 36 (78%) dogs with chronic disseminated histoplasmosis.8,9 Large bowel diarrhea, characterized by hematochezia, mucus, and tenesmus, is common.11 With disease progression into the small intestine, diarrhea may become watery and voluminous, and protein-losing enteropathy may occur.8-11 In addition to gastrointestinal signs, common nonspeci c clinical signs of chronic disseminated histoplasmosis in dogs include weight loss, inappetence, and fever of unknown origin that is nonresponsive to antibiotic therapy.7-11,20 Abnormal lung sounds, with or without accompanying cough or dyspnea, are noted in fewer than 50% of dogs with disseminated histoplasmosis.11 In ltration of the organism into other organs, including the liver, spleen, and bone marrow, may result in hepatomegaly, splenomegaly, or pallor associated with anemia.8,9 Less commonly reported clinical ndings of canine disseminated histoplasmosis include • Vomiting21-23 • Peripheral lymphadenopathy10,11,24,25 • Polyarthropathy or fungal osteomyelitis10,11,26,27 • Ulcerated dermal nodules, sores on footpads, or draining abscesses10,21,28-32 Serum chemistry profile Hypoalbuminemia was reported in ve of ve cats and nine of 11 dogs with dis- 250 May 2008 VETERINARY MEDICINE
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.