Inability to close the jaw implies a bilateral lesion affecting the motor component of the trigeminal nerve (mandibular branch of CN V) since a unilateral lesion will not cause sufficient weakness to prevent mouth closure. The bilateral nature of the trigeminal nerve lesion implied that it involves the peripheral nerves rather than the cranial nerve nuclei (brainstem lesion) since a lesion in the brainstem large enough to affect both trigeminal nuclei would likely be fatal. The loss of sensation in the described region of the face indicates bilateral lesion of the sensory component of the trigeminal nerve (maxillary and ophthalmic branches CN V).
Considering the multifocal lesion localisation, differentials should include inflammatory/infectious disease and multifocal neoplastic processes. Idiopathic trigeminal neuropathy (also called trigeminal neuritis, trigeminal neurapraxia or trigeminal nerve palsy) is the main differential. Other neurological causes for bilateral paralysis of the mandibular branch of the trigeminal nerve include multicentric lymphosarcoma (neoplastic lymphoid cell infiltration), myelomonocytic leukaemia, idiopathic hypertrophic chronic pachymeningitis, disseminated, non-suppurative ganglioradiculoneuritis and rabies.
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