History
A 2-year-old 42.8-kg spayed female Labrador Retriever presented for progressive painful swellings of 1 month’s duration over the lumbar dorsum with lethargy and hyporexia. Fine-needle aspirate consisted of RBCs and a low number of neutrophils and macrophages. Previous treatment with cefpodoxime, carprofen, and marbofloxacin (dosages not reported) did not alleviate the signs. On physical examination at Eclipse Specialty and Emergency Pet Care Hospital, soft fluctuant swellings of 5 to 10 cm that were painful to the dog were noted over the entire dorsal lumbar subcutaneous tissue. No skin discharge or cutaneous defects were found. The rectal temperature was normal, and a CBC revealed a mild neutrophilia (11.72 X 103 cells/µL; reference range, 2.95 X 103 to 11.64 X 103 cells/µL) and serum biochemistry a mild elevation in ALT (170 U/L; reference range, 10 to 125 U/L). The prothrombin and partial thromboplastin times were normal. Radiographs of the caudal abdomen were obtained (Figure 1).
Left lateral (A) and ventrodorsal (B) radiographic views of the caudal abdomen in a 2-year-old Labrador Retriever evaluated for painful subcutaneous swellings of the lumbar subcutaneous tissue.
Citation: Journal of the American Veterinary Medical Association 263, 3; 10.2460/javma.24.09.0579
Radiographic Findings and Interpretation
Orthogonal views of the caudal abdomen were obtained (Figure 2). There were coalescing, wispy soft tissue opacities throughout the subcutaneous space dorsal to the lumbar spine, pelvis, and included tail, which gave the subcutaneous space a heterogenous “lacy” appearance. This was also seen in the subcutaneous space along the left and right aspect of the abdominal wall and hemipelvis on the ventrodorsal view. No bony abnormalities were seen, and the included abdomen was within normal limits. No foreign material was seen. Differential diagnoses included a subcutaneous nonradiopaque foreign body, infection, inflammation, neoplasia, edema, and hemorrhage.
Left lateral (A) and ventrodorsal (B) radiographic views of the same dog as in Figure 1, with white arrows pointing out the lacy subcutaneous tissue with swelling.
Citation: Journal of the American Veterinary Medical Association 263, 3; 10.2460/javma.24.09.0579
Treatment and Outcome
To further evaluate for a foreign body, a pre- and postcontrast CT scan was performed (Figure 3). Throughout the subcutaneous space, there were coalescing soft tissue to fluid densities that appeared as amorphous mass-like regions. Some of these regions exhibited peripheral contrast enhancement. The larger regions appeared in contact with the adjacent epaxial musculature.
A—Cross-sectional postcontrast CT image of the same dog as in Figure 1 at the level of the sacroiliac joint (white arrowhead) showing subcutaneous tissue swelling (white arrow). Window width, 400 HU; window level, 40 HU; 1.3-mm slice thickness. B—Sagittal postcontrast CT image of the same dog as in Figure 1 at the left ilial wing showing subcutaneous tissue swelling (white arrow). Window width, 400 HU; window level, 40 HU; 1.3-mm slice thickness. D = Dorsal. L = Left. R = Right. V = Ventral.
Citation: Journal of the American Veterinary Medical Association 263, 3; 10.2460/javma.24.09.0579
Differential diagnoses included subcutaneous neoplasia such as hemangiosarcoma, mast cell neoplasia, or cutaneous lymphoma; steatitis; foreign body; vasculitis; subcutaneous abscesses; seromas; and hematomas resulting from an infectious or immune-mediated disease process. Differential diagnoses also included (much less likely) bruising from coagulopathy.
Two separate surgical biopsies were obtained from the dorsal and left lateral lumbar skin and subcutaneous tissues. Bacterial culture was negative, and the histopathology revealed lymphoplasmacytic to pyogranulomatous inflammation with pannicular fibrosis. No foreign material, fungal organisms, or bacteria were noted. The diagnosis was consistent with sterile panniculitis.
Treatment with a 3-month prednisone taper (1 mg/kg, PO, q 12 h for 30 days; then 1 mg/kg, PO, q 24 h for 30 days; then 1 mg/kg, PO, q 48 h for 30 days. depending on response to taper) and Vitamin E (8 U/kg, PO, q 24 h indefinitely) were started. On a phone call 3 weeks later, the owner reported an increase in appetite and decrease in swelling with better energy.
Comments
The radiographs in this case showed increased soft tissue opacity within the subcutaneous tissue of the lumbar area with no apparent radiopaque foreign material or calcified mass, suggesting a diffuse disease process which required further investigation. The CT was utilized to investigate if a foreign body or area of mass was present to provide focus for surgical exploration.1 The CT images were useful in confirming no intra-abdominal extension of disease and planning where to obtain biopsy samples from the most thickened areas of the subcutaneous tissue. Sterile panniculitis should be on the differential diagnosis list in dogs with diffuse or multiple areas of painful subcutaneous swelling, and radiographs and CT imaging can be useful to rule out other causes and plan tissue sample procedures.
Sterile panniculitis is thought to be an autoimmune disease.2–4 Dogs will present with painful swellings under the skin, sometimes with ulceration or draining tracks. Pain with lethargy and decreased appetite is common.2 Concurrent polyarthritis, lymphadenitis, or pancreatitis can be seen but were not found in the current case.3 Bacterial and fungal cultures are routinely negative in these cases, and a diagnosis should include skin and subcutaneous tissue histopathology. The subcutaneous fat and panniculus muscle can contain lymphocytes, plasma cells, macrophages, and fibroblasts on cytology and histopathology.2 This variety seen on histopathologic samples likely represents the ebb and flow of intense inflammation followed by scar tissue formation.
The disease process in dogs can be lifelong, with waxing and waning clinical signs.2,3 As with other autoimmune diseases, treatment may need to be continuous in some dogs or intermittent in others. Immunosuppression with prednisone, cyclosporine, and azathioprine have been used successfully.2 Supplemental treatment with Vitamin E as an anti-inflammatory or tetracycline and niacinamide as immunomodulators requires further investigation.
Acknowledgments
None reported.
Disclosures
The author has nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.
Funding
The author has nothing to disclose.
References
- 1.↑
Lamb CR, Pope EH, Lee KC. Results of computed tomography in dogs with suspected wooden foreign bodies. Vet Radiol Ultrasound. 2017;58(2):144-150. doi:10.1111/vru.12457
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O’Kell AL, Inteeworn N, Diaz SF, Saunders GK, Panciera DL. Canine sterile nodular panniculitis: a retrospective study of 14 cases. J Vet Intern Med. 2010;24(2):278-284. doi:10.1111/j.1939-1676.2009.0449.x
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Schissler J. Sterile pyogranulomatous dermatitis and panniculitis. Vet Clin North Am Small Anim Pract. 2019;49(1):27-36. doi:10.1016/j.cvsm.2018.08.003
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Contreary CL, Outerbridge CA, Affolter VK, Kass PH, White SD. Canine sterile nodular panniculitis: a retrospective study of 39 dogs. Vet Dermatol. 2015;26(6):451-458, e104-e105. doi:10.1111/vde.12247
