Weak gluteus maximus and weak iliopsoas with normal gluteus maximus: Two complementary new signs to diagnose lower limb functional weakness

Background and purposeThe diagnosis of functional neurological disorder should be actively made based on the neurological signs. We described two new complementary signs to diagnose functional weakness of the lower limb, weak gluteus maximus (weak GM) and weak Iliopsoas with normal gluteus maximus (weak iliopsoas with normal GM), and tested their validity. MethodsThe tests comprised Medical Research Council (MRC) examinations of the iliopsoas and GM in the supine position. We retrospectively enrolled patients with functional weakness (FW) or structural weakness (SW) who presented with weakness of either iliopsoas or GM, or both. Weak GM means that the MRC score of GM is 4 or less. Its complementary sign, weak ilopsoas with normal GM, means that the MRC score of ilopsoas is 4 or less, whereas that of GM is 5. ResultsThirty-one patients with FW and 72 patients with SW were enrolled. The weak GM sign was positive in all 31 patients with FW and in 11 patients with SW, that is, 100% sensitivity and 85% specificity. Therefore, the complementary sign, weak iliopsoas with normal GM, was 100% specific for SW. DiscussionAlthough 100% should be discounted considering limitations of this study, these signs will likely be helpful in differentiating between FW and SW in the general neurology setting. Downward pressing of the lower limb to the bed in the supine position is interpreted by the patient as an active movement exerted with an effort and might be preferentially impaired in FW.

Automated summary

This study describes two new signs, weak gluteus maximus (weak GM) and weak iliopsoas with normal gluteus maximus (weak iliopsoas with normal GM), for diagnosing functional weakness of the lower limb. The tests involved Medical Research Council (MRC) examinations of the iliopsoas and GM in the supine position. These signs showed high sensitivity and specificity in differentiating between functional weakness (FW) and structural weakness (SW).