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As the occurrence of restless legs syndrome (RLS) in diabetes is controversial, the aim of this study was to assess the prevalence of RLS in a cohort of patients with diabetic neuropathy and to analyze the features of the associated neuropathy. We investigated the occurrence of RLS diagnosed in accordance with the criteria of the International Restless Legs Syndrome Study Group in a cohort of patients with polyneuropathy and mononeuropathy multiplex associated with diabetes mellitus (DM), or impaired glucose tolerance (IGT), or impaired fasting glucose (IFG) in a retrospective study. RLS was present in 33/99 patients with neuropathy associated with DM/IGT/IFG (84 with distal polyneuropathy and 15 with multiple mononeuropathy). Comparing patients with or without RLS, small fiber sensory neuropathy was more common in the RLS patients (15/33 vs. 15/66), as were symptoms of burning feet (10/33 vs. 6/66). In several patients, RLS was responsive to neuropathic pain medications. The frequent occurrence of RLS in association with thermal dysesthesias may reflect the involvement of small sensory fibers in the form of hyperexcitable C fibers or A-delta fiber deafferentation. We suggest that RLS may be triggered by abnormal sensory inputs from small fibers, especially involved in neuropathy associated with DM/IGT/IFG. Our data show that RLS is a relevant feature of diabetic neuropathy, as a frequent and potentially treatable manifestation of small fiber involvement in the course of DM and IGT/IFG.

Cryoglobulinemia represents an emerging cause of peripheral neuropathy, especially in Southern Europe, in view of its relationship with hepatitis C virus infection. In a series of 100 consecutive referral patients with uncharacterized peripheral neuropathies, we systematically investigated cryoglobulinemia to assess its diagnostic yield. The most frequent diagnosis was hereditary neuropathy (33%), 29% were acquired neuropathies of different types, and no cause could be identified in 27%. Cryoglobulinemic neuropathy was diagnosed in 11 patients (7 women and 4 men), aged 54-77 (mean = 63.5 years), most presenting with sensory polyneuropathy, often asymmetrical. Cryoglobulin was also detected in 2 additional patients in whom a final diagnosis of non-Hodgkin lymphoma was made. Purpura was absent in 4 patients (and in 2 with lymphoma), or restricted to discrete manifestations in the remaining patients, which did not provide a clue to the diagnosis. Thus, search for cryoglobulin proves useful in a substantial number of undiagnosed peripheral neuropathies (11% to 13% in our series), even in the absence of typical skin lesions, and it is recommended as a first-line investigation in patients with unexplained neuropathy presenting in middle to older age.