Purpose: to find out if a menthol cream containing mannitol is more effective than the same cream without mannitol in relieving painful diabetic peripheral neuropathy (PDPN). The test cream which will, at a later date, be marketed as QR cream contains Water, Mannitol, Propylene glycol, Isopropyl palmitate. Caprylic capric triglyceride, Ceteareth 20, Cetearyl alcohol, Glyceryl stearate, Polyethylene glycol 100 Stearate, Dimethicone, Octyldodecanol, Menthol, Lecithin, Ethylhexyl glycerin, Phenoxyethanol. The control cream contains the same ingredients minus the mannitol.
Hypothesis: a menthol cream containing mannitol is more effective at relieving the pain, the physical limitations and the emotional distress caused by PDPN than the same cream without mannitol.
Justification: PDPN is common and can be disabling because of the intensity of the pain it can cause. Less than 50% of those suffering from this condition get adequate pain relief from their current medications. The oral medications, anticonvulsants, antidepressants, NSAIDS, marijuana derivatives and narcotics have numerous side effects and are potentially addictive. Topical local anaesthetics have short-lived effect over only a small area and topical capsaicin often causes burning on application and prolonged use destroys the affected nerves. A previous study has demonstrated mannitol's effectiveness in down regulating the capsaicin receptor which is believed to cause the burning sensation of PDPN. A cream containing mannitol has few side effects, and, if effective, may decrease the need for other, more dangerous medications.
Objectives: to show that a menthol cream containing mannitol is more effective, over a period of 28 weeks, than the same cream without mannitol at relieving the pain, the physical limitations and the emotional distress caused by PDPN.
Research Design: this is a randomized, double-blind, placebo-controlled crossover trial involving 3 visits.
Participants who are taking medications or insulin to treat diabetes will have on/off vibration test on the hallux of each foot. If at least 5 of their 8 vibration tests are erroneous or "I don't know", their score on the DN4 questionnaire is \>4/10 they will be enrolled.
After 1 month's observation period, 90 participants will be given either a menthol cream with mannitol or the same cream without mannitol to apply to their feet for 3 months, following which the creams will be crossed over for an additional 3 months. Which cream is to be applied in the first 3 months will be chosen at random. Participants and clinicians will be blinded as to cream assignment for the duration of the study. Participants will be instructed to rub the cream on their feet and the tender nerves supplying their feet, 2 to 4 times daily, as needed for pain relief.
At 0,1,4 and 7 month, their BPI pain severity and interference scores, DN4 scores, cream % effectiveness and side effects will be recorded. At 4 and 7 months, they will be compared.
Statistical Analysis: primary endpoint, BPI pain interference scores (how much pain interferes with function and relationships) . t-tests will compare the difference between the maximum daily pain interference score for the menthol cream as compared with the mannitol and menthol cream at 4 and 7 months. Secondary endpoints: BPI pain severity score and DN4 score (how many symptoms of peripheral neuropathy are registered), % cream effectiveness, incidence of side effects.
