Nodular amyloidosis derived from keratinocytes: an unusual type of primary localized cutaneous nodular amyloidosis.

Primary, localized cutaneous amyloidosis includes macular, lichen, and nodular (tumefactive) types in which the amyloid deposits are limited to the dermis without systemic involvement. The material in lichen and macular amyloidosis is derived from epidermal keratinocytes [keratinocyte-derived amyloid (AK)], whereas that in nodular amyloidosis is derived from immunoglobulin light-chains amyloid (AL). Primary, localized cutaneous nodular amyloidosis (PLCNA) is a form of primary, localized cutaneous amyloidosis that has been associated with a risk of progression to systemic amyloidosis. We report an unusual case of nodular AK-type amyloid deposited in the dermis of the feet. The patient is a 60-year-old woman with asymptomatic verrucoid-like lesions present around the medial and lateral aspects of the bilateral heels for 1-2 years. A biopsy showed massive deposition of eosinophilic amorphous material in the papillary and reticular dermis. The material stained positive for Congo red with apple-green birefringence on polarized light. It was also positive for pan-cytokeratin and negative for kappa and lambda light-chain immunostains. An extensive workup was negative for systemic involvement. Lipid chromatography tandem mass spectrometry confirmed that the deposition was AK-type amyloid. We believe that this is the first case of PLCNA with AK deposition. This entity should be included in the differential diagnosis of PLCNA so that an extensive systemic workup may be avoided.