Feline maculopapular cutaneous mastocytosis, also called urticaria pigmentosa, is a rare skin disease of cats. Under the microscope, the affected skin holds clusters of mast cells, often together with eosinophils [1]. Mast cells and eosinophils are immune cells that take part in allergic and inflammatory reactions. This is not the same as a mast cell tumor, which is a lump. For that, see mast cell tumors in dogs and cats.
If your cat has a rash, bumps or crusts on the skin, see your vet. Other skin diseases can look the same.
What you may notice
A case series of 13 cats sorted the signs into three patterns [1]:
- bigger raised bumps and welts, mostly on the head, shoulders, underside of the neck and armpits, which in some cats faded on their own;
- a red rash of small flat spots and bumps, often with crusts, which tended to last longer;
- a slow, long-lasting form where the skin becomes thick and darker in color.
Thick skin of this kind is called lichenification, and darker skin is called hyperpigmentation.
Which cats get it
Hairless and curly-coated breeds stand out. In that series, nine cats were Sphynx, two were Devon Rex and two were crosses of the two breeds, and more females than males were affected [1]. The authors saw this as support for a breed link [1]. These are findings from one group of cats at one referral clinic.
How vets diagnose it
Your vet may take a skin biopsy, a small piece of skin sent to the lab, to look for the typical mast cell pattern [1]. In the case series, signs had been present for months before the diagnosis was made [1].
Tests matter because ringworm can look like this disease. In a report of three Devon Rex cats with this kind of rash and biopsy pattern, every cat turned out to have ringworm, and the skin cleared once the fungal infection was treated [2]. The authors stressed that telling the two apart changes which treatment is safe [2]. Ringworm (dermatophytosis) is a fungal infection. For more, see ringworm in dogs and cats.
Treatment
Your vet will advise on treatment for your cat. In the case series, cats responded to treatment in different ways [1].
At home, as directed by a vet:
- do not put human or leftover medicines or skin products on your cat unless your vet says so;
- tell your vet about any new bumps, crusts or changes in the skin;
- go back for any recheck your vet books.
When to see your vet
See your vet if your cat has:
- raised bumps, welts, flat spots or crusts on the head, neck, shoulders or body [1];
- any rash or skin change you are unsure about.
The bottom line
Urticaria pigmentosa is a mast cell skin disease reported mostly in Sphynx and Devon Rex cats. Only a vet can tell it apart from ringworm and other skin diseases that look the same.
This article is for general information only and does not replace advice from your veterinarian. If your cat has a rash or crusted bumps, see your vet.
Sources
- Ngo J, Morren MA, Bodemer C, Heimann M, Fontaine J. Feline maculopapular cutaneous mastocytosis: a retrospective study of 13 cases and proposal for a new classification. J Feline Med Surg. 2019;21(4):394-404. PubMed abstract, National Library of Medicine. PMID 29860905. https://pubmed.ncbi.nlm.nih.gov/29860905/
- Colombo S, Scarampella F, Ordeix L, Roccabianca P. Dermatophytosis and papular eosinophilic/mastocytic dermatitis (urticaria pigmentosa-like dermatitis) in three Devon Rex cats. J Feline Med Surg. 2012;14(7):498-502. PubMed abstract, National Library of Medicine. PMID 22736683. https://pubmed.ncbi.nlm.nih.gov/22736683/