Introduction: In amyotrophic lateral sclerosis (ALS), lateral hand muscles, the abductor pollicis brevis (APB) and the first dorsal interosseous (FDI), are usually more affected than the medial hand muscle, namely the abductor digiti minimi (ADM). This unusual pattern of muscle weakness and atrophy is called the split-hand syndrome, which can be demonstrated by the split-hand index (SHI), calculated from compound muscle action potential (CMAP) amplitudes. Our study developed a novel dynamometric index (DI), which is calculated from the muscle forces, as an alternative method to SHI. Purpose: The purpose of this diploma work was to compare the SHI to DI and to define the correlation between them as well as their diagnostic utility. Methods: 13 ALS patients and 14 healthy sex and age matched controls were included in the study. CMAP amplitudes were obtained by motor nerve conduction studies. The SHI was derived by multiplying the CMAP amplitudes recorded from the APB and FDI muscles and dividing this product by the CMAP amplitude recorded from the ADM muscle. Muscle forces were measured by hand-held dynamometer and used to calculate the DI by multiplying the APB and FDI muscle forces and dividing this product by the ADM muscle force. The indices were compared using the unpaired t-test and nonparametric Mann-Whitney test. Pearson's and Spearman's correlation coefficient were used to examine the relationship between the indices. Receiver-operator characteristic curve analysis of SHI and DI was performed to determine the area under the curve and cut-off values of the indices. Results: The SHI and DI were significantly lower in ALS patients. A strong correlation (rs = 0,8376, p < 0,0001) was observed between the indices in ALS patients. SHI cut-off value of 5,4 with 77 % sensitivity and 96 % specificity and DI cut-off value of 29,5 with 62 % sensitivity and 79 % specificity moderately differentiate ALS patients from healthy controls. Discussion and conclusion: The SHI is more sensitive and specific for determining split-hand patterns in ALS patients. Dynamometry is patient friendlier and DI showed moderate diagnostic accuracy.
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