Cerebral. The neurologist should be alert to signs of dementia (e.g., inattention, memory dysfunction, apathy, disorientation) in patients presenting with olfactory dysfunction, since decreased ability to smell is among the first signs of Alzheimer's disease and is also seen in some patients with Huntington's chorea, multi-infarct dementia, and Pick's disease. Evidence of fainting spells or blackouts, disorientation, seizure activity, and mood change should be sought because both increases and decreases in olfactory function are found in patients with temporal lobe epilepsy. Olfactory loss, along with short-term memory problems and associated confabulation, may help to define vitamin B-, deficiency and the Wernicke-Korsakoff syndrome. Cognitive alterations (e.g., mental slowing, confusion, depression, and hallucinations) may also signal the presence of pernicious anemia.
Cranial Nerves. Optic disk examination and documentation of increased intraocular or intracranial pressure (papilledema) should be obtained because tumors in the olfactory groove or sphenoid ridge (e.g., meningiomas) can cause the Foster Kennedy syndrome, which is composed of three clinical hallmarks--ipsilateral anosmia or hyposmia, ipsilateral optic atrophy, and contralateral papilledema. Although rare, visual disturbances are caused by some forms of sinusitis, which can also alter chemosensation. For example, optic neuropathy has been reported secondary to cocaine-induced osteolytic sinusitis. y Altered visual contrast sensitivity, color perception, and perception of the visual vertical may provide additional information about a more diffuse chemosensory disorder. Hearing problems may reflect viral or bacterial infections in the middle ear that alter taste function in the anterior tongue via chorda tympani nerve (CN VII) damage or inflammation, as well as more general nasal sinus infections that also influence olfaction. Specifically, patients with Korsakoff's syndrome have deficits not only in memory and olfactory function but also in color discrimination and several measures of auditory perception, including dichotic listening tasks. Pupillary reaction to light is also sluggish in patients with this syndrome,
and horizonal nystagmus and ophthalmoplegia, usually involving the bilateral lateral recti in isolation or with other extraocular muscle palsies, are also commonly present.
Applying small drops of sweet, sour, bitter, and salty tasting stimuli (with water rinses between applications) to the fungiform papillae on the front of the tongue (which are innervated by the chorda tympani division of CN VII) and on the circumvallate papillae at the rear of the tongue (CN IX) can be useful in identifying regional deficits and damage to specific nerves involved in taste perception. Iatrogenic factors, such as tonsillectomy, can damage CN IX fibers and produce taste distortions, whereas alterations in CN VII function (i.e., the chorda tympani nerve) can be caused by middle ear infections. Local factors (e.g., dryness, inflammation, edema, atrophy, abnormal surface texture, leukoplakia, erythoplasia, exudate, erosion, and ulceration) can influence taste function through a variety of means (e.g., gastric reflux), as can poor oral health and the use of smokeless tobacco. y
Motor/Reflexes/Cerebellar/Gait. Attention to ataxia, apraxia for orolingual movements, oculomotor abnormalities, coordination problems, gait disturbances, tremor, bradykinesia, and rigidity is critical, since alterations in the ability to smell are present in some patients with Huntington's chorea and multiple sclerosis, and in approximately 90 percent of patients with early-stage Parkinson's disease. In Korsakoff's syndrome, ataxia of the trunk but not of the limbs is frequently present, as are signs of acute alcohol withdrawal (e.g., tremor, delirium, and tachycardia).
Sensory. Decreased position, vibratory, temperature, and pain appreciation occurs in several neuropathies associated with hyposmia. These include diabetes, the neuropathy of renal and hepatic failures, and a large variety of toxic neuropathies. In patients with pernicious anemia, the large myelinated central fibers carrying position and vibration senses are preferentially affected. In the context of hepatitis, the acquired immune deficiency syndrome (AIDS), and other virus-related illnesses, hyposmia can occur along with an ascending polyneuropathy of the Guillain-Barre type. In seizure patients with uncal or temporal lobe foci that induce dysosmic auras, altered sensations in a hemibody distribution can occur as part of the seizure or as a postictal transient sequela.
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