A patient shows weakness, atrophy, and fasciculations of the right tongue and lower face, along with right vocal-fold weakness and nasal regurgitation; these signs are most consistent with damage to which part of the nervous system?

• A. Brain stem
• B. Cerebellum
• C. Left cerebral cortex
• D. Right cerebral cortex

Answer: (A)

Key idea: this combination of findings points to a brainstem problem affecting the cranial nerve nuclei on the right side. The tongue shows weakness with atrophy and fasciculations, which are signs of lower motor neuron involvement of the hypoglossal nerve (CN XII). The vocal fold weakness and nasal regurgitation reflect weakness of palatal and laryngeal muscles, mediated by the vagus nerve (CN X) via the nucleus ambiguus in the medulla. When both XII and X are impaired on the same side, the lesion is localized to the brainstem, specifically the medulla on the right.

Cortical lesions would produce different patterns, typically UMN signs and absence of focal LMN signs like fasciculations in the tongue. Cerebellar lesions cause coordination problems rather than LMN weakness of cranial nerves. So the most consistent location is the brainstem, on the right side.