This patient had a small area of infarction in his left thalamus that involved the somatosensory nuclei (ventral posterolateral and ventral posteromedial) where spinal cord and brainstem sensory pathways terminate. Therefore, all modalities of somatic sensation were impaired on his right side. His distressing over-response to cold stimuli was an example of a thalamic pain syndrome. Presumably, it reflected abnormal overactivity somewhere in the system for processing painful stimuli that was secondary to thalamic injury, but the details are not known.
Spontaneous pain syndromes can result from lesions in other parts of the CNS, and by themselves do not localize the lesion to the thalamus. In this patient, other neighboring parts of the thalamus and its fiber connections were spared. The various thalamic nuclei provide critical inputs to specific region of cortex. Lacunar strokes involving the thalamus can produce other deficits ranging from extrapyramidal movement disorders to aphasias.