Motor evoked potentials in unilateral lingual paralysis after monohemispheric ischaemia
Ludwig Boltzmann Institute for Epilepsy and
Neuromuscular Disorders, Second Department of Neurology, Neurological
Hospital of Vienna, Rosenhuegel, Vienna, Austria
Correspondence to: Dr Wolf Muellbacher, Second Department of Neurology, Neurological Hospital of Vienna, Rosenhuegel, Riedelgasse 5, 1130 Vienna, Austria. Telephone 0043 1 88000 266; fax 0043 1 88000 384.
Received 27 January 1998 and in revised form 29 April 1998;
Accepted 15 May 1998
OBJECTIVES
The occurrence of a lingual paralysis
after unilateral upper motor neuron lesions is an infrequent clinical
phenomenon, and the underlying pathophysiological mechanisms are poorly
understood. We studied the cortical motor representations of
ipsilateral and contralateral lingual muscles in healthy controls and
in a selected group of stroke patients, to clarify the variable
occurrence of a lingual paralysis after recent monohemispheric ischaemia.
METHODSA special bipolar surface electrode was
used to record the ipsilateral and contralateral compound muscle action
potentials (CMAPs) from the lingual muscles after transcranial magnetic
stimulation (TMS) of the human motor cortex and peripheral
electrical stimulation (PES) of the hypoglossal nerve medial to the
angle of the jaw. Four patients with a lingual paralysis (group 1) and
four patients with symmetric lingual movements (group 2) after
monohemispheric first ever stroke were studied and compared with 40 healthy controls.
RESULTSIn controls, TMS of either
hemisphere invariably produces CAMPs in the ipsilateral and
contralateral lingual muscles, elicited through crossed and
uncrossed central motor pathways, respectively. In the 40 healthy controls, TMS of either hemisphere elicited CMAPs of
significantly greater amplitudes and shorter onset latencies from the
contralateral muscles compared with the ipsilateral responses (p<0.0001). In the patient groups, TMS of the affected hemisphere failed to evoke any CMAP from either lingual side; TMS of the unsevered
hemisphere always produced normal ipsilateral and contralateral responses, irrespective of whether the ipsilateral muscles were paralysed or not.
CONCLUSIONSBilateral crossed and uncrossed
corticonuclear projections are invariably existent in humans. After
unilateral interruption of these pathways, some people do exhibit a
lingual paralysis whereas others do not. The development of a central
lingual paralysis is most likely dependent on the ability of the
unsevered hemisphere to utilise the pre-existent uncrossed motor
projections. The variable availability of these pathways among
individual subjects is in good agreement with the inconstant occurrence
of a lingual paralysis after restricted monohemispheric lesions.
© 1998 by Journal of Neurology, Neurosurgery, and Psychiatry
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