Characterization of Transient Alterations of Cutaneous Sensory Nerve Function by Cryolipolysis

Overview

Cryolipolysis with Zeltiq CoolSculpting device is a novel method of non-invasive fat removal. The technique works by application of cold plates to the skin surface for a single cooling cycle lasting 60 minutes, after which a cold-induced inflammatory panniculitis leads to selective loss of fat. There is no histologic evidence of necrotic or inflammatory damage to skin or nerves, however a single small human study has reported prolonged temporary altered sensation (hypoesthesia) in the area of cryolipolysis procedure. This hypoesthesia seen in about 2/3 of patients, is completely reversible, lasts up to 8 weeks after treatment, and suggests that cooling under these conditions can temporarily alter sensory nerve function. The purpose of this study is to further characterize the reversible cutaneous sensory function alteration after cryolipolysis with Zeltiq CoolSculpting device. Using multiple modalities of sensory nerve function we hope to elucidate the details of cryolipolysis induced sensory nerve alteration.

Study design We undertook an open-label, prospective study at the Massachusetts General Hospital (MGH) (Boston, USA) between December 2012 and July 2013. The study was approved by the MGH Institutional Research Board and was registered at ClinicalTrials.gov (NCT01673113). Written, informed consent was obtained from all participants prior to participation in the study. The study conformed to the standards set by the Declaration of Helsinki and Good Clinical Practice Guidelines. Eleven healthy subjects were enrolled in the study. They were randomized to have either the left or right flank treated with a single cycle of cryolipolysis. Baseline measurement of sensory function was evaluated using QST at the treated and control (untreated) flank for each subject. Histamine iontophoresis was used to evaluate itch duration and intensity on the treated and control flank for each subject. All sensory function testing, including responses to histamine-induced itch, were assessed at 48-72 hours, and Day 7, 14, 21, 35 and 56 post-treatment. In 6 subjects, skin biopsies (3 mm diameter) for histological analysis of nerve fiber density at the treated flank were taken at baseline, 48-72 hours, Day 21 and 56 post-treatment. Cryolipolysis procedure All subjects received cryolipolysis treatment to the flank above the iliac crest, on one side of the body. The untreated (contralateral) flank served as the control throughout the study. Subjects were randomized to have right or left flank treated and randomization was achieved with a computer-generated randomization code. The treatment site was identified, assessed and marked by a single, unblinded investigator. The sensory testing site within the flanks was marked and registered using a transparent plastic sheet, aligned using cutaneous landmarks including nevi or scars, and photographed with the subject in a standard position, to ensure that the same area was tested on follow-up visits. Cryolipolysis was performed using an EzApp6.3 applicator (CoolScultping, Zeltiq Aesthetics Inc, Pleasanton USA) and standard settings at cooling intensity factor (CIF) of 41.6, corresponding to heat transfer of -73mW/cm2, applied for one hour. Quantitative sensory testing (QST) The QST protocol consisted of a series of 7 sensory tests. The QST procedure started with the evaluation of mechanical followed by thermal thresholds.