Role of insulin-like growth factor-I in the treatment of painful small fiber predominant neuropathy

Abstract

Idiopathic, painful, small fiber predominant peripheral neuropathy is resistant to symptomatic treatment. Previous treatments have not been directed toward repairing the underlying deficit. Growth factors hold promise as agents to encourage axonal regrowth. In vitro, insulin-like growth factor-I (IGF-I) has been shown to prevent neuronal apoptosis, to increase axonal growth, and to support myelination. Using a double-blind, placebo-controlled design, 40 patients were randomized to treatment with recombinant human IGF-I (0.05 mg/kg twice daily by subcutaneous injection) or placebo for 6 months. There were no significant adverse events and minor adverse events occurred equally in both groups. The primary outcome measure was change in score on an analog pain scale. Secondary endpoints included quantitative sensory testing, quantitative autonomic testing, neuropathy impairment score, nerve conduction studies, and neuropathy symptom and change score. There was no significant difference in the primary endpoint between the two groups. Analysis of secondary endpoints and a global impression of improvement by patients and physicians did not show consistent differences between the groups. IGF-I was safe, but did not improve symptoms in this 6-month trial.