Split-hand plus sign in ALS: Differential involvement of the flexor pollicis longus and intrinsic hand muscles

Abstract

The flexor pollicis longus (FPL), a key muscle involved in fractionated thumb movements, may be relatively spared in amyotrophic lateral sclerosis (ALS) compared to the thenar group of muscles, termed the split-hand plus sign. Consequently, the diagnostic utility of the split-hand plus sign was prospectively assessed in ALS. In total, 103 patients (37 ALS and 66 non-ALS) with neuromuscular symptoms underwent assessment of FPL and APB strength using the Medical Research Council (MRC) score. A median nerve strength index (MSI) was developed to quantify differential involvement by expressing the APB strength score as a fraction of the FPL strength score. The APB muscle strength was significantly reduced compared to FPL strength in ALS patients (p < 0.0001), but was comparable in the non-ALS disorders (p = 0.91). In addition, there was a significant reduction of MSI scores in ALS patients (MSI_ALS 0.8; MSI_non-ALS 1.0, p < 0.01). Analysis of receiver operating characteristic (ROC) curves disclosed that MSI < 0.9 exhibited an area under the curve of 0.86 (p < 0.001) with a sensitivity of 85% and specificity of 86% for limb-onset ALS. In conclusion, split-hand plus sign distinguished ALS from non-ALS neuromuscular disorders, thereby suggesting a diagnostic utility of this novel clinical sign in ALS.

Key words::

• Biomarker
• neuropathology
• excitotoxicity

Acknowledgements

Steve Vucic serves on the scientific advisory board for Novartis, Merck Serono Australia and Bayer Schering Australia. He also serves as a medical consultant for Merck Serono Australia.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Funding support from the Motor Neuron Disease Research Institute of Australia (MNDRIA), Sylvia and Charles Viertel Charitable Foundation Clinical Investigator grant, Ramaciotti Foundation and National Health and Medical Research Council of Australia is gratefully acknowledged.