Reverse Split Hand Syndrome: Dissociated Intrinsic Hand Muscle Atrophy Pattern in Monomelic Amyotrophy Spectrum Disorder (P4.100)

Objective: We report a clinically useful sign with its electrophysiological signature and also discuss its diagnostic utility in diagnosing monomelic amytrophy spectrum disorder. Background: Monomelic amyotrophy spectrum disorder is a form of focal anterior horn cell disease affecting adolescent and young adults. Diagnosis is mainly electro-clinical. Methods: 30 individuals were recruited with 10 in each group of monomelic amyotrophy (MMA) spectrum disorder, amyotrophic lateral sclerosis (ALS) and normal healthy controls. In MMA group mean age at presentation was 25.88 (range 19-30) years and disease duration of 8.12 years, ALS had mean age 51.86 (40-67 ) years with mean duration of 11.14 months, controls had mean age of 25.29 (Range 22-29) years. Split hand syndrome is severe weakness and atrophy of abductor pollicis brevis/ first dorsal interossei (APB/FDI) complex and relative preservation of abductor digiti minimi (ADM) seen in ALS while opposite pattern is termed as reverse split hand syndrome. Ratio of APB/ADM was chosen to electrophysiological define split and reverse split hand with low and high values respectively. Reults: All MMA patients had clinical reverse split hand syndrome while split hand syndrome was observed in 7 ALS patients, in other 3 there was uniform and severe hand involvement. In NCS, MMA showed preserved CMAP of APB in all patients with severe involvement of ADM which was absent in 3 individuals. APB amplitude was severely reduced in all ALS patient patients, while relative preservation was noted in ADM amplitude. All MMA patients and controls had APB/ADM ratio>0.8 but it was >1.4 in 80 [percnt] of MMA while in normal controls values were near 1 (none had>1.4). All ALS patients had values <0.8 and 70[percnt] had below 0.6. Conclusion: In conclusion we report an interesting and pathognomonic electroclinical sign in patients with MMA which may provide useful diagnostic clue to this focal anterior horn cell disorder. Disclosure: Dr. Singh has nothing to disclose. Dr. Nalini has nothing to disclose.