Our search found 37 bedside clinical tests or groups of tests for motor FND (functional weakness and functional movement disorder) that had some formal validation (table 2). Sample size varied between 8 and 107 patients with FND. Most investigations of positive signs were conducted in a single study or a small number of studies (maximum five for the Hoover sign), allowing for the calculation of pooled specificity and sensitivity by merging data from different studies. Five studies reported on the inter-rater reliability of positive signs.

Overall, the specificities of validated signs are high, ranging from 64% to 100%; however, the sensitivities are lower, ranging from 9% to 100%. Inter-rater reliability of these signs is overall good to excellent (defined as values: <0.2 poor/0.21-0.4 fair/0.41-0.6 moderate/0.61-0.8 good/>0.8 excellent).

General signs common to all FND presentations are: variability of the symptom, which can be observed during history taking and examination, and effortful or grimacing expression while following the examiners instructions during examination. If suspecting a functional movement disorder, test oculomotor function to show abnormal eye movements and in particular convergence spasm,100 even if the patient did not endorse this as a concern during history taking.

When assessing gait, look for typical positive signs such as monoplegic leg dragging, excessive visible effort (huffing and puffing sign),50 falling toward support (chair nearby, table, wall), excessive slowness, hesitation or caution, non-economic posture (for example knee flexed), and knee buckling (sudden loss of tone at each step).101 Asking a patient with severe gait disorder to propel a chair while sitting on it will show improvement in FND.51

When assessing hemifacial spasm, look for typical signs such as long contraction of more than three seconds, lip pulling (tonic deviation of the lip, often the lower one) sometimes with platysma contraction, and lack of other Babinski sign for hemifacial spasm (other Babinski sign=eyebrow elevation on the side of the spasm).102 Positive signs for functional orofacial movements in comparison with tardive dyskinesia are: lack of chewing movements, lack of self-biting, lingual movements without mouth movements, and abnormal speech.45 A large case series (61 patients) that focused on facial functional movement103 reported involvement of the lip as the most frequent (60.7%, with the lip pulling feature).

When assessing movements of the trunk, look for the typical positive sign of asymmetry in strength of the sterno-cleido-mastoid muscle.53 A functional Romberg sign is described as large movements of imbalance with sudden steps and no falls and improvement with cognitive distraction or numbers drawn on the back.48

When assessing episodes of cataplexy (brief, symmetrical loss of muscle tone with retained consciousness precipitated by strong emotions) look for positive signs54 such as lack of sudden facial expression change, facial jerks or grimaces, postural dyscontrol (head drop, trunk fall), in addition to preserved tendon reflexes (which typically disappear during cataplexy associated with narcolepsy).

When assessing upper arm weakness, look for discordance or inconsistency in strength (at different instances during the examination), as well as a give-way/collapsing pattern, drift without pronation, and/or co-contractions of agonist and antagonist muscles preventing movement of the tested joint. As a cautionary note, give-way/collapsing pattern of weakness is common in patients with pain limited weakness (and pain limited weakness should not be mistaken for functional limb weakness).104 In cases of complete hand plegia, involuntary abduction of the fifth finger can be seen when the patient is asked to do a forced abduction against the examiners resistance on the healthy hand.58 The flex-ext sign, which is the equivalent of the Hoover sign,105 can be elicited as follows: the involuntary flexion of the arm at the elbow that occurs when the patient focuses on extending the healthy elbow against the examiners resistance is better than the voluntary flexion.59

When assessing lower limb weakness, also look for discordance/inconsistence, give-way/collapsing weakness, co-contractions, and the Hoover sign.61 The classical way to describe a positive Hoover sign is when the involuntary hip extension (when the patient focuses on flexing the healthy leg against the examiners resistance) is stronger than the voluntary hip extension. A similar pattern can be found during leg abduction60: when the patient is asked to do a forced abduction with both legs against the examiners resistance, the weak leg will have a stronger involuntary abduction than when the voluntary abduction is tested. In patients with severe unilateral leg weakness, positioning passively the leg in flexion with the soles on the bed (spinal injury test)62 shows a discordance in strength as the weak leg will not fall on the side, as expected in complete weakness.

When assessing tremor, typical signs are distractibility, entrainment, and increase in amplitude with weight load on the wrists. In addition, look for variability in amplitude, frequency, and direction of tremor.63 A whack a mole sign can be seen106: when the limb affected by tremor is immobilized by the examiner, the tremor appears in another body segment (head, trunk, other arm, or legs).

No validated clinical signs are available for assessing dystonia, but a pattern of adult sudden onset fixed dystonia (typically clenched fist sparing thumb and index finger107) or equinovarus foot is suggestive of functional dystonia.108 Associated prominent pain and other FND signs can help support the diagnosis.109

When assessing tics, no validated signs are available but clinical clues can help identify functional tics110111: lack of premonitory urge and inability to suppress the movement, female preponderance, additional FND symptoms, lack of response to anti-tic medication, and absence of family history. In functional tics, the cranial region is less affected, the type of tic is often blocking (ie, interferes with voluntary action) and pali, echo, and copro phenomenon are less common.

Overall, the evidence for rule-in motor signs shows very high specificity, which advocates for their routine use in clinical practice. A range of educational pictorial and video libraries illustrate many of these signs.2101102112113 Too much emphasis on a single sign, however, can lead to false positives. In a cohort of 190 patients diagnosed with a neurological disorder, 37 (20%) had at least one positive functional neurological sign.91 Interestingly, regression analysis showed that this 20% of the cohort had typical risk factors known in patients with FND, suggesting that the presence of positive signs in this subgroup could either be false positives or indicate the presence of an FND comorbidity. Keep in mind the possibility that the patient has both FND and another neurological disorder: recent reports describe functional neurological signs in a subset of patients with Parkinsons disease114115 or multiple sclerosis.116 Overall, data from a systematic review and a prospective study underscore that rates of misdiagnosis in FND since 1970 (once confirmed) are low, and between 1% and 4%.117118

Recently, efforts have been made to integrate additional clinical features in the process of diagnosis, such as, for example, abrupt onset, fluctuations of the motor symptom, comorbid pain, and fatigue.119 The presence of these features should raise the index of suspicion and prompt a more systematic search of signs positive for FND.

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Diagnosis and management of functional neurological disorder - The BMJ