Foot‐Hand Synkinesis in Corticobasal Syndrome: Single Clinical Feature with Distinct Molecular Imaging Biomarkers

Hand-foot synkinesis in a patient with phenytoin intoxication

“…Although cerebellar dysfunction is common in phenytoin intoxication, hand-foot synkinesis has not been reported as a clinical manifestation of this condition. The contribution of secondary motor areas, including the SMA, dorsal and ventral premotor cortex, and cingulate gyrus to hand-foot synkinesis has been suggested in several case reports and a functional MRI study [2] , [3] , [4] . The hand and foot areas are separated in the primary motor cortex but overlap in the secondary motor areas.…”

“…A potential association between cerebellar dysfunction and hand-foot synkinesis has not yet been reported. However, in the case of CJD with hand-foot synkinesis, the patient presented with cerebellar signs such as dysmetria on the finger-to-nose test, wide-based ataxic gait, and retropulsion during standing [2] . Moreover, fluorodeoxyglucose-positron emission tomography showed hypometabolism not only in the SMA and premotor cortex but also in the right cerebellum.…”

“…Hand-foot synkinesis is an involuntary movement of the foot induced by the movement of the unilateral hand, or vice versa [1] , [2] . This neurological sign is seen in patients with Parkinson’s disease (PD), essential tremor, Creutzfeldt-Jakob disease (CJD), and corticobasal syndrome [2] , [3] , [4] . Herein, we report the first case of phenytoin intoxication that led to hand-foot synkinesis.…”

A Reflection on Motor Overflow, Mirror Phenomena, Synkinesia and Entrainment

“…The most common form of synkinesia is the facial synkinesia, commonly occurring after Bell's palsy 58 and clinically characterized by contraction of additional facial mimetic musculature (ie, eye closing) accompanying volitional facial movements such as smiling or chewing; however, other types of synkinesia have also been described. These include the ocular‐jaw synkinesia (observed in PD, characterized by jaw movements ipsilateral to the horizontal gaze deviation), 59 the respiratory synkinesia (also called “breathing arm,” characterized by contraction of one or multiple upper limb muscles together with the diaphragm muscle; usually reported in the context of an upper limb injury) 60 and arm‐leg synkinesia (sporadically reported in patients with frontoparietal or thalamic stroke, 61,62 prion disease, 63 or parkinsonian conditions such as PD and cortico‐basal syndrome) 64 . In this latter case, voluntary hand movement may be accompanied by similar movements in the ipsilateral leg, or vice versa 1,65 .…”

“…While a motor task performed with the hand was associated with activation of hand motor cortex in control subjects, the additional activation of foot motor cortex and of the ipsilateral SMA was also evident in patients in whom this hand motor task determined similar movements in the ipsilateral foot (hand–foot synkinesia) 67 . On these basis, the main hypothesis regarding the development of arm‐leg synkinesia is related to the dysfunction of secondary motor areas, such as the premotor cortex, SMA, cingulate cortex, and their connections to the primary motor cortex 1,64 . Indeed, the arm and leg regions overlap considerably in the secondary motor cortical areas, thus it is possible that synchronous motor neuron activation in the arm and leg areas within the primary motor cortex may be maintained by the common input from the secondary motor areas rather than an increased horizontal connectivity within the M1 area 63 …”