Answer 6

The unilateral atrophy of temporalis and masseter muscles as well as reduced jaw tone implies a lesion of the ipsilateral motor component of the trigeminal nerve (mandibular branch of CN V which innervate the temporalis, masseter, rostral digastricus and pterygoid muscles). Right-sided enophthalmia and partial protrusion of the third eyelid likely reflects passive retraction of the eyeball secondary to loss of temporalis and digastric muscle mass. The decrease tear production is likely secondary to involvement of the ophthalmic branch of CN V which causes loss of afferent (sensory) stimulation to the lacrymal reflex. The lesion localisation is therefore right-sided trigeminal nerve. Differentials include mainly trigeminal nerve sheath tumour and neuritis.

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