The Auricular Blind Spot: Primary Cutaneous Amyloidosis as a Diagnostic Contender

Summary: A 69-year-old man presented with two white to skin-colored papules in the left auricular concha. They were sometimes itchy and irritated, prompting excisional biopsy. Histopathology revealed deposits of amorphous, eosinophilic material in the papillary dermis. Histopathologic differential diagnoses included primary cutaneous amyloidosis (PCA) and colloid milium. Considered together, histopathology and clinical presentation were diagnostic of PCA of the auricular concha. Only a few cases of PCA of the auricular concha have been described in the literature, though it may be underdiagnosed. Clinical differentials often include seborrheic keratoses, flat warts, basal cell carcinoma, and adnexal neoplasms. When evaluating waxy papules on the auricle, PCA should be considered. Though nearly indistinguishable on H&E, PCA of the auricular concha and colloid milium have distinct clinical presentations. Adult-type colloid milium clinically presents as numerous yellow-brown papules and plaques, most often on the periorbital face and sun-exposed areas. PCA of the auricular concha, however, presents as grouped waxy skin-colored papules on the auricle, most often in the conchal bowl. Our case highlights the importance of clinicopathological correlation for accurate diagnosis. Knowledge and recognition of PCA of the auricular concha can help prevent unnecessary additional workup, since it has not been associated with systemic amyloidosis.