Papular eosinophilic / mastocytic dermatis ("Feline urticaria pigmentosa")

Definition:

This is a skin disease, still poorly documented, more frequently described on Sphynx cats and on Humans.

Origin:

On Sphynx cats, it is widely supposed that the disorder is inherited. A study concerning 5 Devon Rex cats with this disease also emphasize a potential genetic origin: the affected cases seem to be those with less hair (which might be more related to the Sphynx phenotype).
It is supposed that this disease is closely related to allergic phenomenon (due to parasites or environment, food allergy.etc.) which could be the trigger factor of the dermatitis.

Clinical features:

The affected cats are young. They have a maculo-papular eruption which is often pruriginous: these are erythematous papules ("red spots"), sometimes crusted, with or without hyperpigmented macula. Their distribution is either linear and symmetric on the ventral lateral side of the trunk or disseminated on the ventral aspect of the thorax and/or the neck. They can cause itching.
Sometimes, a greasy seborrhoea on the head and the dorsum is in more observed.

Differential diagnosis:

Other dermatitis can lead to those skin lesions like atopic dermatitis, food hypersensitivity, flea bite hypersensitivity, dermatophytosis (moth), mast cell tumor, superficial bacterial folliculitis, or Malassezia dermatitis. A recent study (2012) shows that 3 Devon Rex cats who had urticaria pigmentosa-like dermatitis, had also a dermatophytosis. The authors concluded that papular eosinophilic/mastocytic dermatitis in Devon Rex cats may represent either an atypical presentation of dermatophytosis or a clinical and histological reaction pattern to various diseases, including dermatophytosis and allergic diseases. That's why skin examination and analysis are necessary to make the diagnosis.

Histological lesions:

The definitive diagnosis requires skin biopsy. The dermis is infiltrated by well-differentiated degranulated or nondegranulated mast cells and eosinophils (= immune cells involved in allergic reactions).

Treatment:

In general, the condition is successfully controlled with prednisolone (glucocorticoïds) at anti-inflammatory doses, essentials fatty acids oral administration and sometimes with anti-histaminics. The evolution is chronic with ups and downs (some allergies could trigger "attacks"). The condition relapses when the treatments are discontinued but prognosis remains good.
It is currently unknown if, as in the Human condition, it exists a more severe form becoming widespread to other organs.

Prevention:

At present, no selection program exists because the disease is poorly documented on Devon Rex cats. Precautionary principle should dismiss affected cats of the reproduction plans.

 

Source: Papular eosinophilic/mastocytic dermatitis (feline urticaria pigmentosa) in Devon Rex cats: a distinct disease entity or a histopathological reaction pattern? Noli C. et al., Veterinary dermatology (2004) 15, 253-259.