Functional (psychogenic) neurological disorders (FNDs) are common and should be diagnosed using positive diagnostic features of internal inconsistency. However, there is a lack of objective data regarding motor signs and a lack of signs relating to motor disorders that affect the upper body and neck. The objective of this study was to provide specificity and sensitivity data on 2 axial motor signs: the sternocleidomastoid (SCM) and platysma signs.
Thirty patients with motor FNDs according to the Diagnostic and Statistical Manual of Mental Disorders, fifth edition, and 40 organic controls with unilateral weakness were prospectively included. The SCM functional sign and platysma organic signs were systematically tested and compared between groups.
The SCM sign had high specificity of 90% (confidence interval [CI], 77%-96%) to detect FND when the platysma sign had 100% specificity (CI, 88%-100%) for detecting organic weakness. The co-occurrence of a positive SCM and a negative platysma sign in patients with unilateral weakness carried 95% specificity (CI, 83%-99%) and 63% sensitivity (CI, 44%-80%).
The SCM test and platysma signs can be used for the diagnosis of motor FND. The extent to which these add value to other validated signs (such as Hoover's sign) should be further evaluated.