Amyloidoses

The amyloidoses are a group of diseases characterised by extracellular tissue deposit, which shows green polarisation birefringence after Congo red staining. Cutaneous amyloidosis could be restricted to the skin or can be one of the systemic manifestations of the disease. There are three types of cutaneous localised amyloidoses: lichen, macular and nodular amyloidosis. Cutaneous amyloidosis requires differential diagnoses with several cutaneous diseases like lichen simplex chronicus, hypertrophic lichen planus, prurigo nodularis, papular mucinosis, pemphigoid nodularis, epidermolysis bullosa pruriginosa, scleroderma, cutaneous sarcoidosis and primary skin tumours such as basal cell carcinoma, xanthomas granuloma faciale and skin lymphoma. The diagnosis of amyloidosis requires the histological demonstration of amyloid deposits. This is a positive Congo red-stained tissue specimen with the characteristic apple-green birefringence in polarised light. In systemic amyloidosis, abdominal subcutaneous fat aspiration or biopsy of minor salivary glands are convenient and a non-invasive method that demonstrates amyloid deposits in 70–85 % of patients. The diagnosis of cutaneous localised amyloidosis is based on the presence of amyloid fibrils in skin biopsy. In macular and lichenoid forms, the amyloid deposits are confined to the papillary dermis. In nodular cutaneous amyloidosis, the amyloid deposits are located in the papillary, subpapillary and reticular dermis, with infiltration of the blood vessel wall.