History

A 5-year-old 23-kg female spayed Border Collie mix was presented to the Misawa Air Base Veterinary Treatment Facility for evaluation of progressively worsening left thoracic limb lameness of 3 months duration. The dog originated from South Texas and then resided in Alaska for 3 years prior to living in Japan. The dog initially presented to another clinic 1 week prior, where left forelimb radiographs were performed. The CBC completed at the initial clinic revealed a mild eosinopenia (0.04 X 10³ eosinophils/µL; reference range, 0.06 X 10³ to 1.23 X 10³ eosinophils/µL) and mildly elevated globulins (4.8 g/dL; reference range, 2.4 to 4.5 g/dL). Canine C-reactive protein was mildly elevated (1.1 mg/dL; reference range, < 1 mg/dL). Due to the inability to obtain a definitive diagnosis from the first clinic, the owner sought a second opinion.

On initial examination, the dog was bright, alert, and responsive. Rectal temperature was mildly elevated at 39.3 °C (reference range, 37.5 °C to 39.2 °C) and the dog had a body condition score of 7 on a scale from 1 (extremely emaciated) to 9 (morbidly obese). Cardiac and pulmonary auscultation were within normal limits. All claws appeared small and brittle, and the distal pinnae were bilaterally thickened and alopecic. She displayed an intermittent partial weight-bearing lameness of the left forelimb. There was a firm, warm swelling over the left distal antebrachium including the distal radius and the carpus, with decreased flexion in the carpus, along with generalized atrophy of the left brachial and shoulder muscles.

The dog was seen 1 week after initial examination for carpal arthrocentesis as well as FNA and biopsy of the swelling over the left distal antebrachium. In house differential cell count of the carpal synovial fluid revealed 57% segmented neutrophils, 35% lymphocytes, and 9% monocytes. Synovial fluid culture was negative for aerobic bacterial growth. Cytology of the left distal radius revealed a moderate number of neoplastic mesenchymal cells, suspicious for a malignant mesenchymal neoplasm, most likely osteosarcoma. Bone biopsy obtained from the left distal radius was nondiagnostic. Thoracic radiographs and orthogonal views of the left carpus were obtained (Figure 1).

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Dorsopalmar (A) and lateral (B) radiographic images of the left carpus of a 5-year-old 23-kg spayed female mixed-breed dog that presented for a 1-month history of progressive left forelimb lameness.

Citation: Journal of the American Veterinary Medical Association 2024; 10.2460/javma.24.04.0275

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Radiographic Findings and Interpretation

Radiographs of the left antebrachium display intracapsular soft tissue swelling of the left carpal joints. The distal left radial diaphysis, metaphysis and epiphysis has a moth-eaten lytic pattern of the cortical and medullary bone that imparts a coarse trabecular pattern, with very mild proliferation at the dorsal distal radius. Moth-eaten lysis is also present in the intermedioradial carpal bone, and questionably in the distal ulnar diaphysis, sesamoid bone of the abductor digit I longus, and first carpal bone. Based on the radiographic appearance of the left carpus, differential diagnoses included osteomyelitis (bacterial or fungal) or neoplasia (chondrosarcoma, osteosarcoma, synovial cell sarcoma, other). Each of the digits of the left manus have a very short, lytic to osteopenic ungual process with some of the toenails appearing irregular (digits 3, 4 and 5). Some of the ungual crests are also irregular and misshapen. The proximal phalanx of the first digit and middle phalanx of the second, third, fourth, and fifth digits appear coarse with decreased corticomedullary bone distinction compared to normal (Figure 2). Differentials for the appearance of the digits included systemic lupoid onychodystrophy or systemic lupus. Three-view thoracic radiographs are normal with no significant findings.

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Same radiographic images as in Figure 1. There is marked swelling of the carpal joints, especially the radiocarpal joint (thick arrow). The distal radius diaphysis, metaphysis, and epiphysis has a moth-eaten lytic pattern of the cortical and medullary bone (thin arrow). Moth-eaten lysis is also present in the radial carpal bone.

Citation: Journal of the American Veterinary Medical Association 2024; 10.2460/javma.24.04.0275

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Treatment and Outcome

Referral for additional workup and repeat bone biopsy was offered to the owner but declined. The owner elected to pursue left forelimb amputation based on concern for neoplasia as reported on the cytology results. Left forelimb amputation via scapulectomy was performed and the patient recovered uneventfully and was discharged to the owner. The left distal radius, carpus, and left axillary lymph nodes were submitted for histopathology. Histopathology results revealed that the lesions of the left distal antebrachium and axillary lymph nodes were consistent with granulomatous inflammation centering on Coccidioides immitis spherules. Treatment with itraconazole (4 mg/kg, q 24 h) is ongoing and the patient is doing well 1 year post operatively; at the initiation of treatment following forelimb amputation, the IgG coccidioidomycosis titer was 1:32 and is currently 1:16 after approximately 8 months of antifungal therapy. The presence of small, brittle claws on all 4 feet and lytic pathology observed on radiographs suggest lupoid onychodystrophy or systemic lupus; however, the digits of the left forelimb were not submitted for histopathology, so the etiology is unknown at this time.

Comments

The dimorphic fungi Coccidioides immitis is the causative agent of coccidioidomycosis, which is endemic to the southwest United States. The primary infection in dogs is pulmonary and frequently results in chronic cough. Disseminated disease is common, with bone being the most common site, but cutaneous, cardiac, ocular, nervous system, or other organ disease is also possible.¹ Dissemination can occur early in the disease process or months after initial infection, with the most common clinical presentations being neurologic signs or lameness due to osteomyelitis. Coccidioidomycosis infection in dogs can be difficult to diagnose due to overlapping clinical signs and frequently requires several modalities including radiology, serology, and histopathology.² In the present case, the left forelimb radiographs revealed a moth-eaten lytic pattern of the distal radius and several of the carpal bones, suggesting an infectious etiology or neoplasia. Because multiple bones appeared affected on radiographs, infection or joint-centered neoplasia were considered more likely than a primary bone tumor; however, these findings were incongruent with the cytology sample which did not show inflammation or an infectious etiology and suggested the presence of a mesenchymal neoplasm. Serology can aid in diagnosing Coccidioides infection; however, many clinically normal animals may have positive serology due to prior exposure or infection.³ In nonendemic regions, such as in the present case located in Japan, recognition of the disease can further be complicated by lack of experience and laboratories that provide serologic diagnostic tests.⁴

Forelimb amputation and histopathology provided a definitive diagnosis and removal of the painful lesion in the presented case. If the diagnosis of Coccidioidomycosis were reached earlier, long term treatment with antifungal therapy such as ketoconazole or itraconazole would have been recommended; however, the prognosis of return to normal function of the left forelimb is unknown due to the severity of inflammatory changes present in multiple bones in this limb.⁵

Disclosures

The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.

Funding

The authors have nothing to disclose.