Primary Localized Cutaneous Amyloidosis: A Histological and Immunohistochemical Appraisal
Nithye Parvathy, Rashmi Joshi, Rajsmita Bhattacharjee, Uma N. Saikia, Dipankar De, Debajyoti ChatterjeeAbstract
Background:
Primary localized cutaneous amyloidosis (PLCA) is a rare chronic heterogeneous group of disorders with deposition of abnormally folded beta-pleated protein in the dermo-epidermal junction and dermis. There are three major forms of PLCA, including lichen amyloidosis, macular amyloidosis, nodular amyloidosis, and a rare variant, amyloidosis cutis dyschromica. We aimed to evaluate the role of immunohistochemistry (IHC) in the diagnosis of PLCA.
Patients and Methods:
A retrospective 8-year audit (2017–2024) was performed. All cases of PLCA were subjected to a panel of IHC, including high molecular weight cytokeratin (HMWCK), Kappa and Lambda light chains; and serum amyloid A. The demographic details and clinical features, along with site predilection, were correlated with the pathological subtypes.
Results:
We included 42 cases of PLCA, among which lichen amyloidosis was the most common subtype (50%), followed by macular amyloidosis, nodular amyloidosis, and amyloidosis cutis dyschromica, with a predilection for the upper back. IHC displayed HMWCK positivity in cases of lichen amyloidosis (14/21, 66.7%), macular amyloidosis (7/11, 63.6%), and amyloidosis cutis dyschromica (2/3, 66.7%). All cases of nodular amyloidosis showed light chain restriction using a combination of IHC and direct immunofluorescence.
Limitations:
Retrospective nature of the study, relatively small sample size, and not performing IHC for other small molecular weight keratins.
Conclusion:
The findings in our study confirm that the amyloid in macular amyloidosis, lichen amyloidosis, and amyloidosis cutis dyschromica is derived from epidermal keratinocytes. IHC for HMWCK should be part of diagnostic workup as it can detect very small amount of amyloid deposition, which may be overlooked during routine evaluation. Nodular amyloidosis demonstrates light chain restriction, indicating the need to exclude systemic amyloidosis.