Page 132 - Edited - Webster HEAD AND NECK - part 2-Merge PDF

HN 320

DISORDERS OF THE CRANIAL NERVES: TESTING THEIR INTEGRITY

1. THE OLFACTORY NERVE

The inability to smell things - anosmia - may follow bilateral destruction of the olfactory mucous
membrane following inhalation of toxic vapour, or following a head injury which disrupts the olfactory
nerves. Perhaps surprisingly, if one set of olfactory nerve roots of olfactory bulb or tract is destroyed,
closure of the opposite nostril also renders the sufferer anosmic. In some circumstances, anosmia may be
thought a blessing, but the ability to smell things is not trivial: without its smell, food loses a quality
generally called "savour" (the nearest most of us get to this is when we have a heavy nasal catarrh), and the
rôle of smell in our sex lives is something of which soap, deodorant and perfume and cosmetic
manufacturers are only too well aware. In some occupations smell is crucial (e.g. perfume blending; in the
wine, coffee and tea trades; in cooking) and in others highly desirable (e.g. any job in which awareness of
gaseous effluvia may mean the difference between safety and injury or even life and death).
Clinical testing is rarely necessary unless the patient complains specifically of anosmia. The tests
are simple - the patient is asked to identify, by smelling, ordinary everyday substances from identical small
opaque pots - for example, clove oil, camphor ("moth balls"), coffee grounds. If you wish to test olfaction
on a routine basis, toilet soap is a reasonable substitute, as is tobacco - but as a doctor you shouldn't have
any of that toxic weed about you ….

''A branch of the sin of drunkenness, which is the root of all evil. A custom loathsome to the eye, hateful to
the nose, harmful to the brain, dangerous to the lungs, and in the black, stinking fumes thereof nearest
resembling the horrible Stygian smoke of the pit that is bottomless."

(A Counterblast to Tobacco - 1604. James I of England, VI of Scotland.)

Anosmia is commonly cited in accident compensation claims. One test to distinguish real from
consciously assumed or hysterical (p.61) anosmia is to ask the subject to sniff 0.88 ammonia. The
unpleasant experience afforded by ammonia gas is mediated not through the olfactory nerves, but through
the trigeminal innervation of the nasal mucous membrane: the true anosmic will therefore react as a normal
person, whereas a "false" anosmic will deny any sensation ....

Olfactory hallucinations are usually a sign of pathology in the region of the uncus of the temporal
lobe.

2. SIGNS AND SYMPTOMS FROM THE EYES - THE OPTIC, OCULOMOTOR,
TROCHLEAR AND ABDUCENT NERVES

SEE: HN 170 et seq.

3. THE TRIGEMINAL NERVE

DISTRIBUTION - See summary Fig., HN 321.

CENTRAL LESIONS.

Lesions of the primary motor cortex or genu of the internal capsule may produce some weakness
in the primary muscles of mastication, but this is not marked. Conversely, lesions of the primary motor
cortex and posterior limb of the internal capsule cause contralateral loss of discriminative tactile sensibility
on the opposite side of the face (and mouth and nasal cavities!)

Brainstem lesions have marked effects:

\NewCMedPhysSc\27 HN 320 DisordCranNerves.