When to see a vet urgently
Contact a vet without delay if a skin lesion is accompanied by the following:
- Ulcers, swelling or darkening skin damage spread rapidly.
- The area is very painful or tissue starts to come away.
- Your cat is clearly lethargic, feverish or stops eating.
- Your cat has difficulty breathing, collapses or deteriorates rapidly overall.
If necessary, find a vet near you. These symptoms do not confirm vasculitis on their own, but their cause may need urgent treatment.
Overview
Blood vessels supply tissues with oxygen and nutrients. In vasculitis, vessel walls become inflamed and damaged, causing disturbances in the small blood vessels and localised skin necrosis. In cats, the vessels in the skin and tissue beneath it are most commonly affected, although internal organs can also be involved in some cases.
Vasculitis describes a tissue reaction pattern, rather than identifying what triggered it. A visible skin lesion does not automatically indicate internal organ disease either. Conversely, blood vessel inflammation can occur elsewhere in the body without visible skin changes. The extent of investigations is therefore selected according to the whole clinical picture.
Necrosis means tissue death. It can occur when blood flow and oxygen supply to an area are sufficiently impaired. However, an ulcer's appearance does not reveal whether it is caused by vessel inflammation, trauma, frostbite or another skin disease. These possibilities require different treatments.
Causes
Vasculitis may be:
- immune-mediated or autoimmune, involving the body's reaction against its own blood vessels
- infection-related, following viral, bacterial or parasitic infections, such as FeLV, FIV or coronavirus
- drug-induced, as a rare side effect
- triggered by allergens, such as insect bites, food or medicines
- idiopathic, meaning the cause is unknown
Immune-mediated does not always mean a true autoimmune disease. Inflammation may be triggered, for example, by immune complexes formed from antibodies and antigens. An antigen is a substance or structure to which an antibody binds. If these complexes accumulate in small blood vessels, they can activate an inflammatory reaction and damage surrounding tissue.
The underlying stimulus may be associated with an infection, medicine or another disease, and sometimes it cannot be identified. A link in timing alone does not establish the cause with certainty. Your vet assesses possible triggers alongside a skin tissue sample and other investigations.
Blood vessel inflammation associated with feline coronavirus can occur in feline infectious peritonitis (FIP), but coronavirus infection is not the same as FIP. A positive coronavirus antibody result indicates exposure and does not, on its own, confirm FIP or the cause of vasculitis. The result of another infection test does not replace investigation of the skin lesion either.
Risk factors
- Older cats.
- Cats with chronic infections.
- Animals prone to allergies.
- Long-term medication.
There is limited research on the importance of these risk factors specifically in cats. Older age, a tendency towards allergies or prolonged medication alone do not establish vasculitis. Investigations assess whether symptoms and findings are consistent with blood vessel damage and whether a current underlying disease or exposure can be identified.
Symptoms
Clinical signs depend on the form of vasculitis:
- skin redness and swelling
- patches, ulcers and crusts
- hair loss in affected areas
- skin irritation, pain and itching
- tissue necrosis in severe cases
- general weakness, fever and loss of appetite in systemic forms
Cutaneous vasculitis may cause changes at the edges of the ear flaps, on the tail and on the paw pads, for example. Bruising, redness, sharply defined ulcers and crusting may be visible. Dead tissue can come away, leaving an open lesion. It is useful to check these areas even if the first change is noticed elsewhere.
Licking and scratching caused by itching can increase skin damage. Pain, discharge or an ulcer on a paw pad can alter walking. Tell your vet what the change looked like initially, as an advanced wound looks different from the first red patch.
Complications and consequences
As the disease progresses, there may be:
- chronic skin changes
- spread of inflammation into deeper tissues
- damage to internal organs, such as the kidneys and liver
- deterioration in general condition
The disease does not progress from the skin to internal organs in every cat. The possibility of organ signs depends on the form of vasculitis and the underlying disease. In immune complex disease, the kidneys' small filtering structures can be damaged, allowing excessive protein into the urine. Urine testing can therefore be relevant to the overall assessment even if your main concern is the skin.
Healing of tissue damaged by poor circulation and control of the original inflammation are different things. During treatment, both the development of new lesions and the condition of existing ulcers are monitored. Rapidly increasing lesions or worsening general wellbeing require reassessment of the treatment plan.
Veterinary diagnosis
- Clinical examination and medical history.
- Skin biopsy with histology as the main method.
- Blood tests to investigate systemic causes.
- Viral tests for FeLV and FIV.
- Exclusion of allergic and drug-related causes.
Before the appointment, gather details of all medicines, products used on the skin, dietary changes, infection symptoms and the timing of new lesions. Previous treatments and their effects are also useful information. Photographs can help describe how a skin lesion developed if its appearance has already changed.
Your vet may also assess whether a red area fades under gentle pressure. Bleeding within the skin behaves differently from redness caused solely by dilated blood vessels. This observation helps describe the lesion but does not establish a diagnosis of vasculitis on its own.
Histology means examining tissue structure under a microscope. It shows how cells are arranged in relation to one another and to blood vessels. A skin biopsy therefore provides different information from a surface cell sample. Tissue examination can also help distinguish inflammation, infection and a tumour. A blood test alone does not confirm inflammation of skin blood vessels.
For a biopsy, a small piece of a lesion is taken or, in some situations, an entire small lesion is removed. Local anaesthetic may be used, but sedation or anaesthesia is sometimes needed depending on the site and the cat. The sampling site is closed with stitches where necessary, and separate care instructions are provided.
While waiting for results, monitor for new lesions. Taking a sample does not mean all other treatment must wait: your vet plans pain relief and skin lesion care according to the situation. If your cat's condition changes quickly, contact the clinic before the agreed results or follow-up appointment.
Read more about vasculitis that damages skin blood vessels in Immune complex cutaneous vasculitis in cats.
Treatment and prognosis
Treatment aims to identify and remove the trigger for inflammation where possible. If a drug reaction is suspected, your vet assesses whether medication should be changed. An infection needs treatment appropriate to its cause. Treatment started solely from the skin's appearance may be insufficient if the underlying cause is not addressed.
Medication that modifies or suppresses immune system activity may be needed to control inflammation. Before choosing strongly immunosuppressive treatment, the possibility of infection is investigated, as infectious diseases can cause similar symptoms. Treatment is tailored to the individual; there is no single treatment plan suitable for every cat.
Changes to medication and decisions to stop it are based on treatment response. Inflammation recurs in some situations, so report new redness, ulceration or swelling to your vet. The prognosis depends on the extent of damage, any internal organ involvement and whether the underlying cause can be controlled. Long-term treatment and follow-up may be needed.
Caring for skin lesions at home
Follow the instructions you receive for cleaning wounds and any dressings. Do not apply human creams, alcohol, hydrogen peroxide or other cleaning chemicals to an open lesion on your own initiative. They can irritate tissue or hinder healing. A suitable cleaning method is selected according to the wound's location and depth.
Prevent licking and scratching with protection recommended by your vet. A protective collar may be used if necessary. Monitor wound discharge, smell, swelling and pain, as well as your cat's eating and movement. Stitches coming out of a biopsy site, increasing bleeding or a rapidly worsening lesion are reasons to contact the clinic.
Prevention
- Treat infections early.
- Monitor medication and check compatibility.
- Prevent insect bites, particularly during summer.
- Arrange regular veterinary examinations for cats with chronic diseases.
Not all forms of vasculitis can be prevented because the trigger may remain unknown. Avoiding insects helps only if they contribute to that cat's reaction. Keep medication details up to date, and always report a suspected previous drug reaction before a new treatment is planned.
What it means for owners
Vasculitis is rare but needs attention. Remember:
- The condition may indicate serious internal organ disorders.
- Early diagnosis makes the disease easier to manage.
- Skin ulcers or unusual changes are reasons to seek veterinary attention.
This material is for information only and does not replace veterinary treatment. Contact a vet if your cat develops symptoms.
Frequently asked questions
Is vasculitis always an autoimmune disease?
No. Blood vessel inflammation is a reaction pattern that may involve infection, a drug reaction, immune complexes or another underlying cause. In some cases the cause cannot be identified.
Could an ulcer on an ear flap be vasculitis?
Yes, but trauma, frostbite or a clotting disorder, for example, can cause a similar change. A persistent or spreading lesion in particular needs investigation and often a tissue sample.
Is a blood test enough to diagnose vasculitis?
Usually not. Cutaneous vasculitis is assessed from a tissue sample, while blood and urine tests investigate underlying causes and other organs, among other things. The results complement one another.
Why is infection investigated before immune-suppressing medication?
Infection can cause similar skin changes, and strong suppression of immune defences may then be the wrong treatment. Your vet combines investigation findings and your cat's condition to choose suitable treatment.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Miscellaneous Diseases Affecting the Pinna in Dogs and Cats, Merck Veterinary Manual, accessed 2026-11-03.
- Cutaneous vasculitis in small animals, Veterinary Clinics of North America: Small Animal Practice / PubMed, accessed 2026-11-03.
- Disorders Involving Immune Complexes (Type III Reactions) in Cats, Merck Veterinary Manual, accessed 2026-11-03.
- GUIDELINE for Feline Infectious Peritonitis, European Advisory Board on Cat Diseases, accessed 2026-11-03.
- Skin Biopsy in Cats, VCA Animal Hospitals, accessed 2026-11-03.
- Feline Skin Diseases, Cornell Feline Health Centre, accessed 2026-11-03.
- Care of Open Wounds in Cats, VCA Animal Hospitals, accessed 2026-11-03.