A 55-years-old man was admitted to our inpatient neurological department because of the abrupt occurrence of gait ataxia, dizziness, nausea and vomiting. In addition, he reported a cold sensation in the left hand and forearm and numbness in the right-hand fingers. The only risk factors for cerebrovascular disease were a moderate hypertension and tabagism. At admission, neurological examination revealed gait ataxia with right lateropulsion, a decrease in the vibration sense and a two-point discrimination over the right-hand fingers, and a decrease in painful and thermic sensations in the left hand and forearm. No other neurological signs were present (in particular pyramidal, cerebellar or brainstem signs). The symptoms disappeared in a few days, except for a mild left-hand and forearm thermic hypoesthesia and right-hand numbness. CT scan and extracranial duplex ultrasonography were normal. Brain MRI showed a small lesion in the left, lower medulla oblongata. A careful analysis of the location of the lesion revealed that it was located immediately caudal to the postolivary sulcus and ventral to the inferior cerebellar peduncle in a left paramedian position, sparing the most posterolateral sector. The atypical distribution of the sensory abnormalities is of interest in this patient: the dissociated sensory impairment involving the upper limb (pain and thermal sense in ipsilateral hand and forearm, tactile discrimination and deep sense in contralateral hand and fingers) is explained by the site of the lesion and the anatomy of the lower medulla at level of lemniscal decussation where secondary proprioceptive fibers (also termed "archiform") run from the nucleus cuneatus to the opposite side of the medulla constituting the medial lemniscus. Archiform fibers are somatotopically organized, being fibers from upper limbs located in a lateral position. Furthermore, spinothalamic fibers are arranged in a concentric manner, the most superficial ones proceeding from caudal areas and the most inner from cranial areas. Therefore, a lesion between the two fibers systems, involving the lateral side of the arciform fibers and the medial side of spinothalamic tract, can explain the restricted dissociated sensory syndrome in our patient. Preservation of the nucleus ambiguous (usually involved in upper medullary infarction) may explain the absence of hoarseness and dysphagia. Moreover, the absence of sensory impairment in ipsilateral trigeminal areas and cerebellar signs may be explained by the preservation of the most posterolateral portion of the medulla, where both descending tract/ nucleus of fifth nerve and restiform body fibers are located.
|Issue number||4 SUPPL.|
|Publication status||Published - 2000|
ASJC Scopus subject areas
- Clinical Neurology