Representative PGP9.5 immunolabeled pretreatment images of axons in vertically sectioned punch skin biopsies; stratum corneum of the epidermis is uppermost with dermis below. (Left panel) Biopsy from a 46-year-old man with newly diagnosed multiple myeloma that is devoid of expected axonal innervation at baseline. Quantitation of intraepidermal nerve fibers identified a neurite density of 65/mm² skin surface area, at the 3rd centile for age and diagnostic of small-fiber polyneuropathy. (Right panel) Biopsy from a 54-year-old woman before therapy. Quantitation of intraepidermal nerve fibers identified a neurite density of 325/mm² skin surface area, at the 78th centile for age, which is within the normal range. The patient illustrated on the left has small-fiber polyneuropathy from his underlying myeloma which is present prior to treatment. (Richardson et al. J Clin Oncol. 2009;27(21):3518-3525.)