Primary systemic (amyloid light-chain) amyloidosis masquerading as pseudoxanthoma elasticum: recognizing a novel clinicopathological pattern.

IMPORTANCE: Primary systemic (amyloid light-chain [AL]) amyloidosis has a variety of cutaneous manifestations. In this case, we present a novel clinicopathological pattern of AL amyloidosis. OBSERVATIONS: A woman in her 50s with a history of AL amyloidosis manifesting as macroglossia and bilateral carpal tunnel syndrome presented with skin-colored to yellow cobblestoned plaques to the neck and bilateral antecubital fossa. Although clinical similar to pseudoxanthoma elasticum (PXE), the skin changes were found to be due to amyloid deposition primarily around the pilosebaceous unit but also within the papillary and reticular dermis. Previous reports of PXE-like plaques in AL amyloidosis have been reported as part of a very rare entity termed amyloid elastosis. However, our case demonstrates several important clinical and pathological differences from this entity. Most notably, there was no dermal elastic fiber involvement, limited cutaneous and systemic involvement, and a fairly indolent course with better response to treatment. CONCLUSIONS AND RELEVANCE: Identification of this atypical presentation of AL amyloidosis has important implications for early detection and rapid treatment. The lack of elastic fiber involvement establishes the uniqueness of this case, and further study may be required to determine if this histological finding has prognostic significance.