Dissociative pseudo-ulnar sensory loss in a patient with a focal haemorrhage secondary to cerebral venous thrombosis - A case report.

Introduction: Small cortical strokes can mimic weakness of peripheral nerve lesions. However, isolated sensory deficits involving the fingers due to cortical lesions are rare.

Methods: We present a case of a 46 year old man with cerebral venous thrombosis, and a haemorrhage restricted to the postcentral gyrus, who reported numbness in an ulnar neuropathy-like distribution. Testing of somatosensory (SSEP) and pain-related evoked potential (PREP) was done, and the lesion location was mapped to the template brain.

Results: The patient had impaired touch and pain but preserved proprioception. He had a normal SSEP response but a prolonged PREP. The lesion was mapped to Broadmann areas 1 and 3b of the postcentral gyrus.

Discussion: Sensory cortical representation is such that, the ulnar fingers are medial, and the radial ones are lateral. Also, modality-specific organization is noted with tactile sensation being mapped to areas 1 and 3b, and proprioceptive sensation to area 3a and 2. Thus focal lesions involving the post central gyrus can have selective sensory loss over some fingers and can have selective impairment of some modalities.

Conclusions: We highlight the rare finding of an ulnar-like sensory loss in a patient with cerebral venous thrombosis and the dissociate nature of the sensory loss in isolated cortical lesions.