Neuropathy is a common side effect of chemotherapeutics used for the treatment of multiple myeloma, including vincristine, thalidomide and bortezomib. The neuropathy induced by these drugs is often preferentially small fiber. Small fiber neuropathies are difficult to diagnose and quantify using conventional electromyography. Determining intra-epidermal nerve fiber density (IENFD) in skin biopsies from diabetes and AIDS patients has been shown to be a more sensitive and more specific ancillary investigation to establish the diagnosis of small fiber neuropathy. In this study the investigators aim to establish the sensitivity of IENFD measurements in skin biopsies from patients with multiple myeloma treated with bortezomib.