“Phalanx sign” helps to discriminate MSA-C from idiopathic late onset cerebellar ataxia

Introduction Early diagnosis of MSA-C in patients with late-onset cerebellar ataxia (LOCA) may prove difficult. We therefore describe and evaluate the performance of the new “phalanx sign” (PS), that should be looked for during the nose–finger test to distinguish MSA-C from idiopathic late-onset ataxia (ILOCA). Methods Sensitivity, specificity, positive predictive value, negative predictive value and interrater reliability of PS were assessed in three groups: 21 MSA-C, 23 ILOCA and 20 age-matched healthy subjects. Results PS was positive for 61.9% of MSA-C patients’, 4.3% of ILOCA patients’ and in none of healthy subjects’ evaluations. PS discriminated MSA-C from ILOCA ( p < 0.001) with a sensitivity of 61.9%, a specificity of 95.7%, a positive predictive value of 92.9%, a negative predictive value of 73.3% and a substantial interrater reliability (Kappa = 0.7273). Conclusion PS could be a helpful, easy and reproducible sign for the early diagnosis of MSA-C in patients with LOCA.