Prurigo nodularis consists of two distinct forms: early-onset atopic and late-onset non-atopic.

BACKGROUND

Prurigo nodularis (PN) is a characteristic chronic dermatosis of unknown etiology showing severely pruritic nodules mainly on the extremities. Atopic diathesis has been implicated as a contributing factor.

OBJECTIVE

Our purpose was to analyze the role of environmental allergens from living organisms in the pathogenesis of PN, to report hypersensitivity against various environmental allergens and to relate this to atopic history in 31 PN patients.

METHODS

Positive and negative controls were studied including 52 patients with atopic dermatitis (AD) and 22 healthy controls. RAST, prick tests and scarification patch tests were performed on the patients and specimens from lesions of 8 patients were stained with anti-eosinophil cationic protein (ECP) antibody.

RESULTS

The 31 PN patients were divided into two groups, those with a past or present history of AD (PN + AD patients) and those without (PN-only patients). Twenty patients (65%) had PN + AD (median age at onset 19 years) and 11 (35%) had PN only (median age at onset 48 years). Analyses of serum IgE levels. RAST scores, prick test and scarification patch test results revealed that the PN + AD patients showed hypersensitive reactions to the environmental allergens in a pattern almost identical to that noted in AD without PN. In contrast, most of those with PN only did not show any hypersensitivity reactions to the environmental allergens. Histologically, many activated eosinophils, identified by monoclonal antibody to ECP, were observed only in the dermis of the PN+AD patients, in contrast to few eosinophils in the lesion of PN-only patients.

CONCLUSIONS

These results indicate that there are two forms of PN: an atopic and a non-atopic one. The PN+AD group is closely associated with AD, being accompanied by cutaneous hypersensitivity to various environmental allergens (a pattern similar to that displayed by AD patients) and has a younger age of onset, whereas the PN-only group, which showed a much older age of onset, does not show any such hypersensitive reactions against these allergens.