To investigate why, in spite of a vast variety of treatment agents, the alleviation of pain in patients with diabetic neuropathy is difficult. Previous studies have not used a treatment algorithm based on anatomic site and neuropathophysiological source of the neuropathic pain.
A model that categorizes the types of pain into three groups (superficial, deep, and muscular) was applied in 75 diabetic patients with chronic (> 12 mo) painful distal symmetrical polyneuropathy in a controlled case series. Twenty-two patients were untreated and 53 patients were treated with imipramine ± mexiletine for deep pain, capsaicin for superficial pain, and stretching exercises and metaxalone ± piroxican for muscular pain. Each type of pain was scored separately on a scale of 0 (none) to 19 (worst), and the total of all three types was used as an index of overall pain. Ability to sleep through the night was scored by a scale of 1 (never) to 5 (always).
No significant differences were observed in initial pain scores, sleep scores, demographics, biochemistries, or physical findings between the two groups. After 3 mo a significant improvement in scores was noted in the treated but not the untreated patients. In addition, a significant difference was found in the change of scores between the treated and untreated patients: total pain (−18 ± 2 vs. 0 ± 2), deep pain (−7 ± 1 vs. 0 ± 1), superficial pain (−5 ± 1 vs. 0 ± 1), muscular pain (−6 ± 1 vs. 0 ± 1), and sleep (1.2 ± 0.2 vs. 0.2 ± 0.2), all P < 0.0001. In treated patients 21% became pain-free (total pain < 2), 66% had improvement (decrease in total pain > 5, but not total elimination of painful symptoms), and 13% were considered treatment failures (a decrease in total pain of < or = 5). This compares with 0 (P < 0.02), 10 (P < 0.0001), and 90% (P < 0.0001), respectively, in the untreated patients.
This study presents a new rationale and hypothesis for the successful treatment of chronic painful diabetic peripheral neuropathy. It uniquely bases the treatment algorithm on the types and sources of the pain.