Common Cranial Nerve Deficits – Figuring Out the Floppy Face

Cranial nerve deficits are frequently encountered in general practice and can present as a single, unilateral deficit or as a component of a more generalised disorder, with potential involvement of multiple cranial nerves +/- the peripheral nerves to the limbs. This lecture will focus on a logical approach to the most commonly affected cranial nerves in general practice; the trigeminal (V) nerve and facial (VII) nerve. The approach to cases with unilateral and bilateral masticatory muscle atrophy will also be discussed. With the exception of the olfactory (I) and optic (II) nerves, the cranial nerves have nuclei within the brainstem where their cells bodies reside, and a peripheral, axonal component that runs to/from the sensory receptors, target glands or muscles. The first step in every case with a cranial nerve deficit, should be to perform a full neurological examination to determine whether the lesion is more likely to involve the cell bodies within the brainstem (termed a ‘central lesion’), or the axonal component outside the brain (termed a ‘peripheral lesion’). This is important to plan the most appropriate diagnostic investigations, and to guide treatment and expected prognosis. [...]