Prevalence and treatment of painful diabetic neuropathy

Abstract

The prevalence of diabetes is rising globally and, as a result, its associated complications are also rising. Painful diabetic neuropathy (PDN) is a well-known complication of diabetes and the most common cause of all neuropathic pain. About one-third of all diabetes patients suffer from PDN. The reported prevalence of PDN varies from 11% in Rochester, Minnesota, USA to 53.7% in the Middle East. One UK study, published in 2011, reported that the prevalence of PDN was 21.5% in type 2 diabetes patients and 13.4% in type 1 diabetes patients, resulting in an overall prevalence of 21%. Numerous studies have found cardiovascular risk factors—including increased age, longer duration of diabetes, higher weight, smoking, poor glycaemic control, renal impairment and high cholesterol—to be associated with PDN. This disorder has a huge effect on people’s daily lives both physically and mentally. Despite huge advances in medicine, the treatment of PDN is both challenging for physicians and distressing for patients. In this thesis, three studies were carried out on the following topics: prevalence and characteristics of painful diabetic neuropathy, PDN patients’ quality of life, and treatment employing lignocaine.
This first study assessed the prevalence of painful diabetic neuropathy (PDN) and its relationship with various cardiovascular characteristics in diabetes subjects. This was done through an observational study of diabetes subjects in Northwest England, UK (n =204). The self-completed Leeds Assessment of Neuropathic Symptoms and Signs questionnaire was sent by post to the subjects and used to diagnose PDN. Consent for participation and access to blood results was given by the study participants. Ethical approval for the study was also granted by National Research Ethics Committee UK. The results of the study showed that the crude prevalence of PDN among subjects was 30.3%. The prevalence of type 2 diabetes subjects was higher (33.1 %) than that of type 1 diabetes subjects (14.1%). There was a significant association of obesity, smoking and height in males with PDN compared to the non-PDN group (P <0.05). The results also showed a significant trend of increasing PDN prevalence with duration of diabetes, increasing HbA1c and increasing BMI (P<0.05). There was a trend of increasing prevalence with age as well (P>0.05); however, due to the small sample size, the data was not statistically significant. There was no relationship of PDN with systolic or diastolic blood pressure, nephropathy, alcohol intake or blood cholesterol (P>0.05). These results highlight the importance of better control of modifiable factors, including smoking, glycaemic control (HbA1c) and obesity.
The second study assessed the impact of painful diabetic neuropathy on quality of life (QoL), mood and anxiety by comparing patients suffering from painful diabetic neuropathy (PDN group) with diabetes patients not known to have PDN (control group, C). The study used short form (SF) 36 and Hospital Anxiety and Depression Scale (HADS Scale) questionnaires. For the PDN group, 25 adult subjects (mean age 56, standard deviation (SD) +/- 11 years, male 15, female 10) were randomly selected from patients attending the painful diabetes neuropathy clinic at Chorley Hospital. For the control group, 25 adult diabetic subjects (mean age 56, SD +/- 14 years, male 14, female 9) were randomly selected from patients undergoing General Practitioner Surgery. Both groups completed the HADS and SF36 questionnaires. Subjects in the PDN group had significantly lower SF36 summary scores in both the physical health (P ˂0.0001) and mental health domains (P= 0.026) compared with the C group. HADS data showed that 56% subjects in the PDN group could be diagnosed anxiety compared to only 20% in the C group (P=0.018); and 60% of the PDN group received the diagnosis of depression compare to 44% in the C group (P=0.396). The results also show that PDN was significantly associated with impaired QoL, both physically (p<0.0001) and mentally (p<0.026). Anxiety was significantly associated with the PDN group compared to control (p<0.018), and depression was 16% more prevalent in PDN group than in the control group.
The final study assessed the efficacy of lignocaine infusion as a treatment for PDN in challenging cases where conventional treatment had not helped. A total 11 patients participated; 7 patients were referred from the pain clinic (non-PDN group), and 4 were referred from the foot clinic (PDN group). All were given lignocaine infusion as a treatment for chronic pain. Participants from both groups were on multiple pain medications with minimal results. All participants gave consent for participation and filled out a McGill short form (SF) questionnaire before and after lignocaine infusion. The results showed a 33% reduction in the visual analogue pain score after lignocaine infusion in PDN group compared to an 11% reduction in the non-PDN group. The data were statistically significant (P<0.05). Similarly, there was significant (p<0.05) reduction of affective pain score: 41% after lignocaine infusion in PDN group, compared to 21% in non-PDN group. In contrast, no significant difference was seen between groups for the sensory pain score reduction after lignocaine infusion: 23% in PDN group compared to 17% in non-PDN group (P>0.05). None of the 11 patients reported adverse effects from the treatment and their observations were within normal limits throughout the lignocaine infusion. Overall, the study showed that lignocaine infusion is effective and safe in reducing the chronic intractable pain when conventional treatments are intolerable or unhelpful. The treatment is also more effective for painful diabetic neuropathy than for other forms of chronic pain.