“Chewy” is a 7-year-old male neutered mixed breed dog presenting with non-pruritic lesions on both ear pinnae.
Andrew Simpson, DVM, DACVD
VCA Aurora Animal Hospital, Aurora, IL
The owners report that prior to this year, there have been no signs of skin disease or itchiness. The onset of lesions was acute and have lasted approximately 2 months prior to presentation. There are no other areas of skin affected and he has experienced mild, intermittent hemorrhaging from the crusted areas on the pinnae.
He was just evaluated 1 month ago by the primary care veterinarian for an annual wellness examination and a 3-year rabies vaccination.
Current medications: Simparica (sarolaner) given by mouth once monthly year-round for flea and tick control, Heartgard Plus (ivermectin + pyrantel pamoate) given by mouth once monthly year-round for heartworm and intestinal parasite prevention.
Objective:
Body Weight: 18.6 kg
Temperature: 101.3 F
Pulse: 124 bpm
Respiratory: 40 bpm
BAR
General examination: no lesions on examination of oral cavity; heart and lungs auscult clearly in all fields with no arrhythmias noted; no lymphadenopathy, abdomen is soft and non-painful on palpation; normal fundic examination; no neurologic abnormalities noted.
Dermatologic examination: both ears have areas of alopecia, adherent crusting, and atrophy of the distal, cranial margin of the pinnae.
Differential diagnoses for pinnal alopecia and crusting: sarcoptic mange, demodicosis, pinnal vasculitis/vasculopathy, dermatophytosis, allergic dermatitis with secondary yeast and/or bacterial infection, idiopathic seborrhea, and sebaceous adenitis.
Diagnostics:
- Deep skin scrapings: no mites present
- Tape cytology: no significant findings, no inflammatory cells, no infectious organisms
- DTM Fungal culture: no growth of dermatophytes
- 4 DX test (heartworm, Lyme, Anaplasma, Ehrlichia): negative
- Skin biopsy of pinnal margin under general anesthesia: smudging of collagen, atrophy of the hair follicles, dermal edema, few intramural neutrophils noted within blood vessels.
Assessment:
Diagnosis: Pinnal vasculitis likely secondary to rabies vaccine
The skin biopsy results were supportive of vasculitis given various changes including follicular atrophy, dermal edema, smudging of the collagen, and inflammatory cells noted with the blood vessel walls. Given the lack of pruritus, allergic dermatitis and sarcoptic mange appeared less likely. There were no biopsy findings consistent with idiopathic seborrhea or other similar seborrheic conditions (i.e. Vitamin A-responsive dermatosis, zinc-responsive dermatosis, etc.). Given the timing of the pinnal lesions in relation to the rabies vaccine, in addition to an otherwise systemically healthy patient and no evidence of tick-borne disease, the likely cause of the vasculitis is a drug reaction to the rabies vaccine.
Treatment:
To address the inflammation more acutely, a tapering course of prednisone was started at 2 mg/kg by mouth split twice daily. This was tapered over 6 weeks. Pentoxifylline was also prescribed as a TNF-α inhibitor to help reduce inflammation in addition to improving microcirculatory blood flow to the pinnae.
Outcome:
The scaling and crusting of the pinnae completely resolved and the hair regrew by approximately 80%. After the prednisone was discontinued, pentoxifylline was continued for 6 additional months and then discontinued without relapse of disease. It was advised to no longer administer the rabies vaccine in the future. Rabies antibody titers were monitored yearly thereafter.
Discussion:
Pinnal vasculitis is a cutaneous reaction pattern, rather than a specific diagnosis, which can present as alopecia, erosions/ulcerations, necrosis, hyperpigmentation, scaling, cutaneous atrophy, and “notching” of the tissue along the pinnal margins and medial (concave) aspects of the pinnae. Generalized forms of cutaneous vasculitis can also occur, which affects the paw pads, distal tail tip, pressure areas such as caudal elbows and hocks, claws, oral cavity, face, and ventral abdomen. Other types of lesions in the generalized form include: hemorrhagic bullae, crateriform ulcers, petechiation, edematous plaques, and pitting edema (i.e. extremities).
As vasculitis is a reaction pattern, potential primary causes should be investigated which include: cutaneous drug reaction, vaccine reaction, food allergy, bacterial infection, auto-immune skin disease (i.e. cutaneous lupus), neoplasia, tick-borne diseases, genetic/familial forms, and idiopathic causes.1
Pinnal vasculitis cases (those cases only affecting the pinnae) appear to be more commonly due to idiopathic causes, however, investigating any possible vaccine or drug correlation is important.2 Cutaneous manifestations of vaccine reactions can develop up to 3-4 months after administering a vaccine. Other vaccines have been implicated as the cause for vasculitis, however, the rabies vaccine is more commonly described. Vaccine-associated vasculitis can occur as a localized reaction pattern only at the site of injection (i.e. alopecia, cutaneous atrophy, erythema), however, generalized forms can also develop.
Definitive diagnosis is confirmed by biopsy of the lesional skin. This more often requires general anesthesia or heavy sedation. In addition, the pinnal margin samples typically leave an area of a scarred notch. In addition, true vasculopathic changes (active inflammatory cells within blood vessel walls) may not always be evident, however, other features of ischemic changes can support the diagnosis.
Treatment options for pinnal vasculitis include vitamin E, pentoxifylline, topical or oral corticosteroids, cyclosporine, topical tacrolimus, and off-label use of oclacitinib.3 Rarely, in progressive cases, partial surgical removal of the pinna might be needed. Most cases will respond to immune-modulatory therapy, oftentimes requiring life-long treatment. Drug-induced or vaccine-induced cases may go into remission after discontinuing the offending drugs after prolonged courses of topical and/or systemic therapies. It is important to note that legal ramifications should be considered if a rabies vaccine is not kept current.
References:
1) Innerå M. Cutaneous vasculitis in small animals. Vet Clin North Am Small Anim Pract. 2013 Jan;43(1):113-34.
2) Morris DO. Ischemic dermatopathies. Vet Clin North Am Small Anim Pract. 2013 Jan;43(1):99-111.
3) Colombo S, Cornegliani L, Vercelli A, Fondati A. Ear tip ulcerative dermatitis treated with oclacitinib in 25 dogs: a retrospective case series. Vet Dermatol. 2021 Aug;32(4):363-e100.
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