Histopathological Insights into Primary Localized Cutaneous Amyloidosis: A Case Series

Background Primary Localized Cutaneous Amyloidosis (PLCA) is a rare disorder characterized by amyloid deposition in the skin without systemic involvement. It includes lichen amyloidosis (LA), macular amyloidosis (MA), and biphasic amyloidosis. The pathogenesis is linked to chronic friction, keratinocyte damage, and in some cases, genetic predisposition. Histopathological examination remains the gold standard for diagnosis. Here, we present a series of nine cases of PLCA. Objective This case series aims to establish a correlation between the clinical manifestations of PLCA and the histopathological findings, including special stains, to improve diagnostic accuracy. Identifying these correlations is vital for differentiating PLCA subtypes, guiding treatment strategies, and understanding the underlying pathogenic mechanisms.  Methods A retrospective analysis was conducted at Panimalar Medical College and Hospital, Chennai, India, reviewing nine biopsy-confirmed PLCA cases from January 2023 to December 2024. Clinical data, histopathological features, and staining characteristics (hematoxylin & eosin, Congo red, and crystal violet) were analyzed. Results Out of nine cases, LA was the predominant subtype (seven cases), followed by MA (two cases). Female predominance was observed (male-to-female ratio was 1:2), with an age range of 39-65 years. The upper limbs were the most frequently affected site. Pruritus was exclusively seen in LA, while hyperpigmentation was present in all cases. Histopathological analysis revealed amyloid deposits in the papillary dermis, epidermal hyperplasia, and inflammatory infiltration in LA. Congo red staining demonstrated characteristic apple-green birefringence under polarized light, confirming amyloid deposition. Conclusion The study reinforces the clinical and histopathological distinctiveness of PLCA subtypes. LA is strongly associated with chronic friction and pruritus, whereas MA presents with asymptomatic hyperpigmentation. Congo red and crystal violet stains remain indispensable for diagnosis. Despite advances in histopathology, therapeutic options remain limited, necessitating further research into targeted molecular treatments and genetic predispositions.