Six years ago, this 55-year-old woman noted the abrupt onset of numerous papules that grew into plaques on her lower extremities . Asymptomatic lesions had been increasing in number and size. A skin biopsy was diagnostic of nodular amyloid and treatments included oral 13-cis retinoic acid and topical steroids without improvement. Phototherapy with PUVA and UVB resulted in some flattening of the papules and plaques. A recent medical evaluation showed no evidence of systemic disease, and her family history was negative. Historically, the term amyloid was used to define proteins that shared similar microscopic characteristics and affinity for certain stains. Amyloid proteins are heterogeneous and the diseases have in common deposits of fibrillar proteins in the dermis. Classification is into two main categories – systemic and localized. In systemic amyloidosis, multiple organ systems are involved and precursors are secreted into the circulation and deposited at distant sites. In localized amyloidosis, deposits are limited to a single organ, at or near the site of protein synthesis.
In nodular amyloid, the fibrillar material is believed to derive from local plasma cells, in contrast to lichen or macular amyloidosis, which have keratinocyte-derived amyloid. Plasma cells produce immunoglobulin light chains that are precursors to the amyloid fibril protein termed amyloid L. The issue of clonality of the plasma cells is unresolved. In some cases, plasma cells have been monoclonal, suggesting a neoplastic disorder; however, in other cases, plasma cells demonstrated polyclonality, which usually is a feature of a more reactive process.
Nodular amyloid is rare and presents with single or multiple waxy nodules and plaques on trunk or extremities. Progression to systemic disease has been reported and the lifetime risk is approximately 7 percent . Many patients, approximately 40 percent , have a gammopathy at presentation; however, few progress to systemic disease. Nevertheless, lifelong monitoring is indicated.
Histopathology reveals large masses of amyloid in the dermis and subcutaneous tissue, often with accentuation around the deep vessels and adnexal structures. Plasma cells, sometimes with Russell bodies, are a prominent feature both within the islands of amyloid and at the periphery.
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The reticular dermis is replaced by homogenous eosinophilic, acellular material within which are collections of plasma cells. Plasma cell collections also surround the material which stains brick red on congo red staining. Polaroscopy shows apple-green birefringence. These findings are typical of nodular amyloidosis.