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A 74 year old woman was referred to the neurological department for evaluation of progressive gait disturbance. On admission she complained of alienation and loss of control of her left arm for six months. There were no spontaneous movements without the patient's intention, but she had always to rely on visual cues. For example, when she was cooking, eating, or doing exercises with her home trainer she had to watch her left arm to be sure of its movement. On examination she was alert, fully oriented, and cooperative. Snout and palmomental reflexes were positive. There was no visual, somatosensory, or auditory extinction. Motor examination revealed a mild left sided facial droop and a left sided pronator drift but strength was full and symmetric and there was no lack of spontaneous movement in the left upper limb. The plantar response was extensor on the left. Gait was slow, unsteady, and wide based. The steps were short with reduced step height. Neuropsychological assessment showed fluent speech without dysarthria. Comprehension and reading were intact. Performance in verbal and non-verbal fluency tasks was diminished, and colour-word interference was slightly increased. Long term memory was slightly deficient for verbal and non-verbal material. Visuo-constructive abilities were normal and there was no spatial neglect. There was no apraxia of the left hand for gestures neither on command nor for imitation. Also, there was no agraphia or tactile anomia of the left hand. She could perform bimanual tasks without evidence of intermanual conflict. She did not exhibit grasp reflex in either upper limb, and there was no compulsive manipulation of objects.
There was, however, an inability of one hand to imitate the posture of the opposite hand when visual cues were removed. Furthermore, there was an inability to distinguish the left hand from an examiner's hand when these were placed in the patient's right hand behind the back, which is known as “strange hand” sign (or “signe de la main étrangére”).1 Additionally, an inability to cross locate touch of the fingers was found: the patient was blindfolded and touched by the examiner on one finger either of the left or the right hand. Then she was asked to point to the location of touch with the contralateral hand. The accuracy was impaired for both directions but especially for right to left pointing. However, she was correct when asked to point to the location of touch on the face or trunk.
Magnetic resonance imaging showed internal hydrocephalus (fig 1A) and an old lacunar ischaemic lesion in the right anterior limb of the internal capsule. Transcallosal inhibition was assessed by transcranial magnetic stimulation (TMS) as described previously2 and showed a deficient inhibition particularly from left to right (upper panels “left A” in fig 1B). Cerebrospinal fluid (CSF) pressure was normal during lumbar puncture. After removal of 50 cc CSF the alienation of the left arm, the “signe de la main étrangére” and the impaired cross replication of hand postures completely disappeared. There was also gait improvement, and for a walking distance of 20 m the number of required steps decreased by five and the time needed by 10 seconds. In accord with the clinical finding there was a neurophysiological restoration of the deficient transcallosal function, which now showed a normal inhibition of the tonic EMG activity (lower panels in fig 1B).
Within three weeks the alienation of the left hand and the gait disturbance reappeared. When readmitted to our department identical callosal dysfunction could be ascertained. After shunt implantation there was permanent recovery of callosal dysfunction and gait disturbance.
Various callosal disconnection signs may follow a structural lesion of the corpus callosum. Among others, there is the sign of impaired cross replication of hand postures when visual cues are removed,3,4 the inability to cross locate touch of the fingers when blindfolded,4 and the “signe de la main étrangére” (the sign of the foreign hand) describing a failure to recognise self ownership of the left hand when visual cues are removed.1
We describe a callosal disconnection syndrome with a “signe de la main étrangére”, an impaired cross replication of hand postures, and an inability to cross locate touch of the fingers in a patient with internal hydrocephalus that completely disappeared after removing CSF indicating a functional impairment of the corpus callosum. The finding is substantiated by electrophysiological studies: the transcallosal motor inhibition before CSF tapping showed a deficient callosal function that normalised after CSF removal. Before CSF tapping there was also a functional asymmetry in that the transcallosal information transfer from left to right was more deficient than from right to left (fig 1). The origin of this asymmetry is not clear, but may be attributable to an additional involvement of adjacent white matter on one side. Together with the restoration of transcallosal dysfunction after CSF tapping, this asymmetry was largely reversible too.
In summary, the restoration of electrophysiologically assessed transcallosal inhibition in parallel with the recovery of the clinical symptoms and signs of our patient suggest a reversible, partial interhemispheric somatosensory disconnection syndrome attributable to a functional impairment of the corpus callosum.
To our best knowledge this is the first report that underlines that dysfunction of the corpus callosum in internal hydrocephalus may not only cause electrophysiological2 but also clinical signs of callosal disconnection.
Competing interests: none declared.