Poster

Development of a sensitive, specific quality of life inventory for peripheral neuropathy

A number of generic quality of life (QOL) instruments are available; however, few of them address the specific problems associated with peripheral neuropathy. From years of clinical experience, we postulated a correlation between subjective and relative query information and results of objective neuropathy tests. To explore this possibility, we needed a sensitive and specific QOL questionnaire to inventory symptoms and the effect of symptoms on activities of daily living and their relationship to quantitative testing for diabetic peripheral neuropathy. Our objective was to develop a non-invasive tool not only explicitly tailored to measure QOL in neuropathy, but also sensitive to the different features of the disease – small and large fiber neuropathy as well as autonomic neuropathy – and clinically relevant for the assessment of the severity of the disease and for monitoring the response to therapy.

Methods
We used the Delphi method to construct a 68-item questionnaire that inventories symptoms, signs and impact on activities of daily life (ADLs) that are condition-specific for diabetic neuropathy. We sought to validate this instrument as a whole, each item individually, and several subscales: autonomic, large fiber (motor and sensory), small fiber (sensory), signs/symptoms, and ADLs.

Subjects
We studied 121 subjects in three groups: 44 normal healthy control subjects (controls, age 54 ± 3, 18 men, 25 women), 35 diabetic subjects without neuropathy (DC, age 62 ± 2, 19 men, 16 women), and 42 diabetic subjects with peripheral neuropathy (DN, age 62 ± 3, 20 men, 22 women) according to the ADA/AAN San Antonio 1989 criteria.

Results
The table shows sensitivity, specificity, and group mean scores for the instrument and each of the sub-scales. On mean scores, the DN group had significantly higher scores (p < 0.001 using ANOVA) for all parameters. The large fiber score correlated more strongly than other subscales with the total score and ADLs (r > 0.95, p < 0.0001). 
We examined each individual question for its sensitivity and specificity. Of the 66 original questions, 38 were found to have >90% specificity when compared with normal controls and diabetics without neuropathy. These were then selected to construct a new tool comprised of those unambiguous questions specific for the different components of neuropathy, QOL and ADLs.

Conclusions
The preliminary results of this study demonstrate that the instrument is specific for diabetic neuropathy and sensitive to the different features of the disease. The small fiber subscale and symptom inventory are particularly sensitive to the presence of neuropathy, while the large fiber score affects more actual QOL items. The high correlation between symptoms and objective tests of neuropathy shows that this instrument has the capacity for providing non-invasive clinical guidelines for assessing disease severity and may be useful for evaluating responses to treatment. Further refinement of this simple, non-invasive tool is now called for.

Treatment modalities according to the different features of neuropathy are available in print.

References
• Vinik, AI. Diagnosis and Management of Diabetic Neuropathy. Canadian Journal of Diabetes Care 2000; 24: 56-76.
• Vinik AI, Park TS, Stansberry KB, Pittenger GL. Diabetic Neuropathies. Diabetologia (in print)