Our patient had a unique presentation of Wernekink commissure syndrome with tetra-ataxia, internuclear ophthalmoplegia, and palatal myoclonus at the onset of a caudal midbrain lacunar infarction. To the best of our knowledge, such a case has not been reported in the literature to date. Palatal myoclonus is known to occur as a late phenomenon due to hypertrophic degeneration of bilateral inferior olivary nuclei. It is not the case in our patient with prior right medullary infarction causing degeneration of the ipsilateral inferior olive with the new caudal midbrain infarction affecting the decussation of dentato-rubro-olivary tracts. This may have caused dysfunction of bilateral dentato-rubro-olivary tracts leading to palatal myoclonus at the onset of stroke.
Wernekink commissure syndrome was first described by Lhermitte in 1941 and first published in 1958. It was named after German anatomist Friedrich Wernekink, who gave the description of brachium conjunctivum as a horseshoe-shaped commissure [
11]. The Wernekink commissure consists of two important white matter tracts: the ascending dentato-rubro-thalamic tract and the descending dentato-rubro-olivary tract. The ascending dentato-rubro-thalamic tract connects the dentate nucleus of the cerebellum through the superior cerebellar peduncle to the contralateral red nucleus and thalamus. The descending dentato-rubro-olivary tract connects dentate and interposed nuclei of the cerebellum with the contralateral red nucleus through the superior cerebellar peduncle and the inferior olivary nucleus in the medulla [
12]. Lesions of the Wernekink commissure at the caudal midbrain may damage the dentato-rubro-thalamic or dentato-rubro-olivary pathways, which leads to early or delayed Holmes tremor and delayed-onset palatal myoclonus or tremor, respectively. The clinical presentation varies depending on the vascular distribution of midbrain arterial perforators that arise from the tip of the basilar artery, superior cerebellar arteries, and precommunicating P1 segment of posterior cerebral arteries called
interpeduncular fossa perforators [
13]. Owing to the proximity of the medial longitudinal fasciculus and trochlear nucleus to the brachium conjunctivum and dentate-rubro-olivary tracts, a caudal midbrain infarction either unilaterally or bilaterally can cause bilateral cerebellar ataxia, dysarthria, multidirectional nystagmus, unilateral or bilateral internuclear ophthalmoplegia, and variable eye movement disorders [
1‐
10]. In contrast to the cases previously reported in the literature (Table
1) with palatal myoclonus occurring several months after ischemic stroke, our patient presented with palatal myoclonus from the onset. Matsuo
et al. and Tuna
et al., in their case reports, hypothesized that delayed palatal myoclonus was secondary to lesions involving the Guillain-Mollaret triangle leading to delayed transsynaptic degeneration of bilateral inferior olivary nuclei [
7,
14,
15]. The onset of palatal myoclonus with acute stroke in our patient questions this hypothesis because there was no evidence of left inferior olivary nucleus degeneration seen on imaging (Fig.
1d, arrow). We hypothesize that the cause of early palatal myoclonus in our patient was due to a two-hit mechanism with degeneration of the right olivary nucleus from prior right medullary infarct and acute right caudal midbrain infarct affecting the dentato-rubro-olivary tract on the left side owing to interruption at the decussation, causing bilateral dysfunction and initiating the palatal myoclonus. As described by Bolen
et al. and Mossuto-Agatiello
et al., despite the degeneration of bilateral olivary nuclei, their patients did not develop palatal myoclonus, thus defining the heterogeneity of this syndrome and its unclear pathophysiology [
1,
8]. Vascular neurologists should be aware of this unique midbrain lacunar stroke syndrome presenting with an interesting palatal movement disorder, which can be very disabling for the patient.
Table 1
Clinical and neuroradiological characteristics of paramedian caudal midbrain stroke cases reported in the literature
| 53/M | HTN, HLD, type 2 DM, ESRD, hemorrhagic stroke | Eight-and-a-half syndrome | – | – | + | + | | | Left pontine hemorrhage extending into midbrain | Left |
| 70/M | HTN, DM, HLD, PVD | Left INO | + | + | – | – | Intermittent jaw clonus, visual and auditory hallucinations | Left caudal midbrain | | – |
| 62/M | | Upbeat nystagmus | + | + | – | + | | Caudal midbrain | | – |
| 57/F | | Right INO | – | + | – | – | | Right paramedian caudal midbrain | | – |
| a) 59/F | HTN | Right gaze-evoked horizontal nystagmus | + | + | – | + | | Caudal midbrain | | – |
b) 71/M | Stroke | Left INO | + | + | – | + | Right hemiparesis | Left paramedian caudal midbrain | | – |
| 59/F | HTN | Horizontal nystagmus | + | + | – | – | Dysmetria | Infarction in the central tegmentum of the midbrain at the level of superior cerebellar peduncle decussation | | – |
| 51/M | HTN, CAD | Right INO | + | + | – | – | – | Left paramedian midbrain lacunar | | – |
| 60/M | HTN | Bilateral INO | + | Bilateral extremities and truncal ataxia | Head tremor | + | – | Bilateral caudal paramedian midbrain | | Bilateral |
Mossuto-Agatiello et al. [ 8] | a) 64/M | DM, HTN, MI | – | + | + | – | | | Right paramedian caudal midbrain | | – |
b) 52/a | HTN | – | + | + | – | – | | Left caudal paramedian midbrain | | – |
c) 38/M | | Horizontal nystagmus with skewed eyes, upward gaze restriction,inappropriate convergence | – | + | – | – | Headache, coma with incomplete locked-in syndrome | Basilar artery occlusion with infarction in superior cerebellar peduncles, cerebellar hemispheres and left thalamus (intracranial vertebral artery dissection was possible etiology) | | – |
d) 34/F | Oral contraceptive pills, smoking | Right oculomotor palsy,INO, bilateral horizontal nystagmus | + | + | – | | | Right paramedian caudal midbrain | | Bilateral |
e) 42/M | Basilar tip aneurysm with acute onset of symptom status postrepair | Non-pupil-sparing right oculomotor palsy, left-sided ptosis | + | + | – | – | Tetraparesis | Paramedian caudal midbrain | | – |
| 27/a | Right midbrain cavernous malformation | Double vision, right-sided ptosis | + | – | Delayed Holmes tremor | – | Left hemiparesis | | | Bilateral |
Mullaguri, et al. (our patient) | 53/M | HTN, type 2 DM, HLD, OSA, and previous right medullary infarction | Right INO | + | Tetra ataxia | – | + | – | Right caudal midbrain infarction, right vertebral artery atherosclerosis, and sessile aneurysm of the tip of the basilar artery | | Right |