INTRODUCTION/AIMS: Nerve conduction studies (NCS) are widely used in diagnosing diabetic polyneuropathy. Combining the Z-scores of several measures (Z-compounds) may improve diagnostics by grading abnormality. We aimed to determine which combination of nerves and measures are best suited for studies of diabetic polyneuropathy. METHODS: Sixty-eight patients with type-1 diabetes and 35 controls were included. NCS measurements were taken from commonly investigated nerves in one arm and both legs. Different Z-compounds were calculated and compared to reference material to assess abnormality. A sensitivity-proxy, accuracy-index (AI) and Cohen's d were calculated. RESULTS: Z-compounds with the highest AI consisted of the tibial- and peroneal motor-, and the sural-, superficial peroneal- and tibial medial plantar sensory nerves in one or two legs. All Z-compounds were able to discriminate between diabetic subjects and non-diabetic controls (mean Cohen's d = 1.42 (range 1.03-1.63)). The association between AI and number of measures was best explained logarithmically (R2 = 0.401), with diminishing returns above approximately 14-15 measures. F-wave inclusion may increase the AI of the Z-compounds. Although often clinically useful among the non-elderly, the additional inclusion of medial plantar NCS into Z-compounds in general did not improve AI. DISCUSSION: Performing unilateral NCS in several motor- and sensory lower extremity nerves is suited for the evaluation of polyneuropathy in diabetic patients. The use of Z-compounds may improve diagnostic accuracy in diabetic polyneuropathy and may be particularly useful for follow-up research studies, as single summary-measures of NCS abnormality-development over time. This article is protected by copyright. All rights reserved.
