OTHER CRANIAL NERVE DISORDERS

Disorders of the Sense of Smell

Olfactory nerve (I) disorders are due to interference with access of the odorant to the olfactory neuroepithelium (transport loss), injury to receptor region (sensory loss), or damage to central olfactory pathways (neural loss). The causes of olfactory disorders are summarized in Table 190-2; most common other than aging are severe upper respiratory infections, head trauma, and chronic rhinosinusitis. Although more than half of people between 65 and 80 years of age suffer from olfactory dysfunction that is idiopathic (presbyosmia), it is increasingly recognized that a number of neurodegenerative disorders are accompanied by olfactory impairment. Pts often present with a complaint of loss of the sense of taste even though their taste thresholds may be within normal limits.
TABLE 190-2: Disorders and Conditions Associated with Compromised Olfactory Function, as Measured by Olfactory Testing
22q11 deletion syndrome
AIDS/HIV infection
Adenoid hypertrophy
Adrenal cortical insufficiency
Age
Alcoholism
Allergies
Alzheimer’s disease
Amyotrophic lateral sclerosis (ALS)
Anorexia nervosa
Asperger’s syndrome
Ataxias
Attention deficit/hyperactivity disorder
Behcet’s disease
Bardet-Biedl syndrome
Chagas’ disease
Chemical exposure
Chronic obstructive pulmonary disease
Congenital
Cushing’s syndrome
Cystic fibrosis
Degenerative ataxias
Depression
Diabetes
Down’s syndrome
Epilepsy
Facial paralysis
Fibromyalgia
Frontotemporal lobe degeneration
Gonadal dysgenesis (Turner’s syndrome)
Granulomatosis with Polyangiitis (Wegener’s)
Guamanian ALS/PD/dementia syndrome
Head trauma
Herpes simplex encephalitis
Hypothyroidism
Huntington’s disease
Iatrogenesis
Idiopathic inflammatory myopathies
Kallmann’s syndrome
Korsakoff’s psychosis
Laryngopharyngeal reflux disease
Legionnaires’ disease
Leprosy
Liver disease
Lubag disease
Medications
Migraine
Multiple sclerosis
Multi-infarct dementia
Myasthenia gravis
Narcolepsy with cataplexy
Neoplasms, cranial/nasal
Nutritional deficiencies
Obstructive pulmonary disease
Obesity
Obsessive compulsive disorder
Orthostatic tremor
Panic disorder
Parkinson’s disease (PD)
Pick’s disease
Posttraumatic stress disorder
Pregnancy
Pseudohypoparathyroidism
Psychopathy
Radiation (therapeutic, cranial)
REM behavior disorder
Refsum’s disease
Renal failure/end-stage kidney disease
Restless leg syndrome
Rhinosinusitis/polyposis
Schizophrenia
Seasonal affective disorder
Sjögren’s syndrome
Stroke
Systemic sclerosis
Tobacco smoking
Toxic chemical exposure
Upper respiratory infections
Usher syndrome
Vitamin B12 deficiency

Treatment: Disorders of the Sense of Smell

  • Therapy for allergic rhinitis, bacterial rhinitis and sinusitis, polyps, neoplasms, and structural abnormalities of the nasal cavities is usually successful in restoring the sense of smell.
  • There is no proven treatment for sensorineural olfactory losses; fortunately, spontaneous recovery can occur.
  • Cases due to exposure to cigarette smoke and other airborne toxic chemicals can recover if the insult is discontinued.
  • Preliminary data suggests that pts with hyposmia may benefit from repeated smelling of odors (such as eucalyptol, citronella, eugenol, and phyenyl ethyl alcohol) over weeks or months; the usual paradigm is to smell odors before going to bed and again upon awakening each day.
  • The use of zinc and vitamin A is controversial, and there does not appear to be much benefit beyond replenishing established deficiencies.

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