The correct answer is A. Lichen amyloidosis.

The clinical scenario describes lichen amyloidosis. Lichen amyloidosis is derived from keratin and is the most common form of primary localized cutaneous amyloidosis. It presents as an intensely itchy rash on the shins, thighs, feet, and forearms. Lesions consist of multiple raised spots (papules) that are scaly and red/brown. Papules may coalesce into thickened plaques.

Nodular primary cutaneous amyloidosis: Also known as amyloidosis cutis nodularis atrophicans and tumefactive amyloidosis. Nodular primary localized cutaneous amyloidosis is the rarest form of primary localized cutaneous amyloidosis. Lesions present as single or multiple firm nodules or plaques may occur on the trunk, limbs, extremities, face, and genitals.

Macular amyloidosis: Macular amyloidosis is one of three forms of primary localized cutaneous amyloidosis. A proteinaceous material, also keratin derived amyloid, is deposited harmlessly in the skin, causing hyperpigmented patches. These lesions are less papular and on pathology lack the epidermal changes such as acanthosis and hyperkeratosis.

Systemic amyloidosis: Primary systemic amyloidosis affects the heart, kidneys, liver, gastrointestinal tract and central nervous system. Skin involvement occurs in about 30–40% of patients.

Amyloidosis cutis chromicum: Amyloidosis cutis dyschromica is a newly described form of primary cutaneous amyloidosis that causes localized hyperpigmentation and hypopigmentation.

 

References: Ladizinski B, Lee KC. Lichen amyloidosis. CMAJ. 2014 Apr 15;186(7):532. doi: 10.1503/cmaj.130698. Epub 2013 Oct 15. PMID: 24130236; PMCID: PMC3986318.