A 49-year-old man presented with a progressively worsening rash on both shins that had been present for 10 years (Figure 1). Nocturnal pruritus interfered with his sleep. He had been using a loofah to scrub his legs when bathing.

Physical examination revealed multiple small, indurated papules on both shins. Some lesions had coalesced into large, scaly plaques. A punch biopsy of the left shin revealed homogenous eosinophilic deposits within widened dermal papillae, with prominent vascularity and pigment-laden macrophages. The results of crystal violet and thioflavin T stains were positive.

Question

Based on the patient's history and physical examination findings, which one of the following is the most likely diagnosis?

• A. Folliculitis.

• B. Granuloma annulare.

• C. Lichen amyloidosis.

• D. Lichen simplex chronicus.

Discussion

The answer is C: lichen amyloidosis, a type of primary cutaneous amyloidosis associated with chronic pruritus. It typically develops after 50 years of age and is more common in patients with darker skin tones. Lesions present as small, hyperpigmented papules that coalesce into larger plaques with a rippled distribution pattern. The lesions are mainly present on extensor surfaces of the extremities, most commonly the shins.