Papular urticaria, which are erythematous lesions with a central crust and may be caused by infestation or insect bites. The lesions are more acute, lack the accentuated skin markings and have a prominent lymphocytic infiltrate with eosinophils within the superficial and deeper dermis.
Lichen planus is characterised by itchy papules but usually these are shiny, violaceous, sharply demarcated and not associated with a central crust. Mucous membrane lesions may coexist. Skin biopsy shows a hyperplastic epidermis with a dense lymphocytic infiltrate which interacts with the basal keratinocytes at the junction.
Multiple dermatofibromas may have a firm central papule and a hyperpigmented margin but are usually nonpruritic, isolated and concentrated on the lower limbs. Skin biopsy shows a hyperplastic epidermis with underlying interlacing bundles of fibroblasts that extend into the deep dermis.
Prurigo nodules is the correct diagnosis and may develop as a distinct phenomenon or in association with atopic dermatitis, persistent insect bites or folliculitis. These papules may herald bullous pemphigoid Metabolic causes such as liver disease, renal failure, thyroid disease or lymphoma may need to be excluded. Treatments include potent topical corticosteroids or intralesional corticosteroids and antihistamines. Ultraviolet light therapy may be helpful when the lesions are widespread In severe cases oral thalidomide (available through the SAS scheme) has been helpful but is often limited by the toxicity of this drug.
Associate Professor Kossard is Director of Dermatopathology at the Skin & Cancer Foundation Australia, Darlinghurst, Sydney, NSW.
This article was first published in Modern Medicine of Australia in January 1999. It was reviewed and updated in January 2011.