Diagnostic role of abductor pollicis brevis -first dorsal interosseous index in diagnosing Amyotrophic lateral sclerosis and comparison of its diagnostic performance with other tests demonstrating split hand phenomenon among Bangladeshi population

BackgroundThe split hand phenomenon is an early and distinctive feature of amyotrophic lateral sclerosis (ALS), resulting from the differential wasting of the intrinsic hand muscles, particularly the thenar muscles. This study aimed to assess the diagnostic role of the APB-FDI Index in the diagnosis of Amyotrophic Lateral Sclerosis (ALS) among the Bangladeshi population. We also compared its diagnostic performances with FDI-ADM and ADM-APB ratios measuring the split hand phenomenon. MethodsWe carried out this cross-sectional study in the Department of Neurology, Sir Salimullah Medical College Mitford Hospital, and Dhaka Medical College Hospital, Dhaka, from March 2019 to September 2021. We determined the APB-FDI index with APB (CMAP) X FDI (CMAP) /ADM (CMAP). We also compared the findings with age and gender-matched healthy control and disease control (Hirayama disease). We studied the value of using APB-FDI, FDI-ADM, and ADM-APB ratios for diagnosis. We analyzed the data with ROC curves and calculated AUC for each ratio. We also used IDI and DCA to compare diagnostic accuracy. ResultsWe studied 43 people with ALS, 30 healthy people, and 10 Hirayama patients. Most ALS patients had cervical phenotypes (31, 72%) and a median ALS functional rating score of 27(IQR,25-32). The cutoff values of APB-FDI Index, ADM-APB CMAP amplitude ratio, and FDI-ADM CMAP amplitude ratio are 4.27, 2.20 respectively. The APB-FDI Index has a high AUC of 0.9, with good sensitivity and specificity. However, for Hirayama disease, the APB-FDI Index cutoff value is 11.6. The APB-FDI Index is clinically effective with optimal threshold probabilities identified through the Youden-Index ((APB-FDI Index-0.72, ADM-APB CMAP amplitude ratio-0.51, and FDI-ADM CMAP amplitude ratio-0.17). Its standardized net benefits exceed healthy control and Hirayama when risk thresholds are between 0.1 and 0.8. The IDI results showed that the APB-FDI Index was superior to the ADM-APB CMAP amplitude ratio and FDI-ADM CMAP amplitude ratio in healthy control and Hirayama although p value is insignificant. ConclusionAPB-FDI Index is the sensitive, specific, and early diagnostic marker for ALS. Its diagnostic performance is better than the other tests.