History
A 4-year-old spayed female mixed-breed dog was evaluated because of a 3-week history of intermittent left forelimb lameness that had been unresponsive to treatment with firocoxib. Physical examination revealed signs of pain in response to palpation of the medial aspect of the left elbow joint and on elbow joint hyperflexion and hyperextension. A CBC revealed a high plasma protein concentration (9.0 g/dL; reference range, 6.0 to 7.8 g/dL). Abnormal findings on serum biochemical analysis included hyperglobulinemia (4.8 g/dL; reference range, 2.5 to 4.0 g/dL), high BUN concentration (26 mg/dL; reference range, 8 to 22 mg/dL), and hyperchloremia (121 mmol/L; reference range, 107 to 115 mmol/L). No abnormalities were detected on urinalysis and ophthalmic examination. Radiography of the left elbow joint (Figure 1) was performed.
Lateral (A) and craniocaudal (B) radiographic views of the left elbow joint of a 4-year-old spayed female mixed-breed dog with a 3-week history of left forelimb lameness.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1373
Same lateral radiographic image as in Figure 1. An osteolytic lesion is seen in the cranial aspect of the radial head with irregular ill-defined periosteal reaction (arrows). No obvious abnormality was seen on the craniocaudal view because of superimposition of the radius and ulna.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1373
Diagnostic Imaging Findings and Interpretation
A faint irregular periosteal reaction is noticeable adjacent to an irregular area of bone lysis at the cranial aspect of the radial head of the left elbow joint (Figure 2).
Computed tomography of the left and right elbow joints was performed. A circular osteolytic lesion with surrounding sclerosis affecting the medial third of the radial head of the left elbow joint was evident (Figure 3); no abnormalities of the right elbow were evident on CT images. An irregular periosteal reaction was observed distal to the lytic area of the left elbow joint (CT scan not shown). Most likely differential diagnoses for this aggressive bone lesion were bacterial or fungal osteomyelitis, with primary or metastatic neoplasia less likely.
Treatment and Outcome
Cytologic evaluation of ultrasound-guided fine-needle aspirates of the lytic lesion of the radial head revealed pyogranulomatous inflammation with numerous phagocytized nonpigmented, septate, branching fungal hyphae that measured 2 to 5 μm in diameter. A diagnosis of osteomyelitis caused by hyalohyphomycosis was made on the basis of the hyphal morphology. Treatment with itraconazole (10 mg/kg [4.5 mg/lb], PO, q 24 h) and tramadol hydrochloride (5 mg/kg [2.3 mg/lb], PO, q 8 to 12 h) was initiated.
At reevaluation 1 month later, ambulation had improved. Physical examination revealed moderate lymphadenomegaly of the left superficial lateral cervical lymph node and popliteal lymph nodes in both hind limbs. Cytologic examination of fine-needle aspirates of all 3 lymph nodes revealed pyogranulomatous inflammation with fungal hyphae that were morphologically identical to those observed in the radial head lesion. The patient was treated with itraconazole and tramadol hydrochloride for 2 additional months, at which time euthanasia was elected because of progressive lameness.
Transverse CT images of the left (A) and right (B) elbow joints of the dog in Figure 1 obtained at the level of the radial head in a bone window (window width, 2,500 Hounsfield units; window level, 480 Hounsfield units). A focal area of hypoattenuation (lysis) surrounded by sclerosis with faint irregular periosteal reaction is present within the craniomedial aspect of the radial head (arrows) of the left elbow joint.
Citation: Journal of the American Veterinary Medical Association 244, 12; 10.2460/javma.244.12.1373
Comments
Fungal osteomyelitis was the most likely diagnosis in this case considering lesion distribution, radiographic findings, and the dog's age. Fungal osteomyelitis typically has a polyostotic distribution to the appendicular or axial skeleton, although monostotic and epiphyseal locations have been described. However, these radiographic findings are nonspecific and primary or metastatic neoplasia must be considered as an additional differential diagnosis.1 Computed tomography is more sensitive for detection of small lytic areas or cortical defects in bone, compared with radiography. As with all aggressive bone lesions, cytologic or histologic examination is necessary for final diagnosis. In addition, radiographic imaging of the thorax is recommended in animals with lytic bone lesions because of the potential for metastasis or fungal pneumonia.
The term hyalohyphomycosis refers to infection caused by molds that are characterized cytologically or histologically by their nonpigmented (hyaline) appearance in tissue. Genera most often reported to cause hyalohyphomycosis in human and veterinary patients include Acremonium, Paecilomyces, Fusarium, Scopulariopsis, Geotrichum, Phialosimplex, and Scedosporium.1 The clinical manifestations associated with hyalohyphomycosis in dogs and cats range from local disease confined to the cornea or skin to disseminated disease involving lungs, kidneys, bone marrow, lymph nodes, liver, spleen, CNS, and bones.2 Historically, disseminated disease and diskospondylitis have been the most common in dogs.3 Because the fungi that cause hyalohyphomycosis are generally opportunists rather than true pathogens, these infections occur more often in human and veterinary patients that are immunocompromised.1 However, hyalohyphomycosis has also been described in animals and people that are apparently immunocompetent, as was the case in the dog of this report.
Osteomyelitis caused by hyalohyphomycosis is typically part of disseminated disease, so surgery is not indicated in most cases. When lesions consistent with fungal osteomyelitis or diskospondylitis are detected, efforts should be made to evaluate other body systems such as lung, spleen, liver, and urinary tract for possible involvement. Medical treatments used most commonly to treat hyalohyphomycosis in small animals include itraconazole and amphotericin B. The newer triazole drugs, voriconazole and posaconazole, may have better efficacy than itraconazole because of their broader spectrum but are considerably more expensive. Treatment of disseminated hyalohyphomycosis with antifungal drugs can prolong survival time4; however, disseminated disease or CNS involvement carries a grave prognosis.
1. Thrall DE. Fungal bone infections. In: Thrall DE, ed. Textbook of veterinary diagnostic radiology. St Louis: Elsevier, 2013; 309–310.
2. Grooters AM, Foil CS. Miscellaneous fungal infections. In: Green CE, ed. Infectious diseases of the dog and cat. 4th ed. Philadelphia: WB Saunders Co, 2012; 675–688.
3. Foley JE, Norris CR, Jang SS. Paecilomycosis in dogs and horses and a review of the literature. J Vet Intern Med 2002; 16: 238–243.
4. Simpson KW, Khan KN, Podell M, et al. Systemic mycosis caused by Acremonium sp in a dog. J Am Vet Med Assoc 1993; 203: 1296–1299.
