Chapter 10

Essentials of Diagnosis

• History of olfactory loss, often manifesting as loss of the sense of taste.
• Sensory evaluation with quantitative tests indicating olfactory loss.

General Considerations

The sense of smell determines the flavor and palatability of food and drink. Along with the trigeminal system, it serves as a monitor of inhaled chemicals, including dangerous substances such as natural gas and smoke, and odors common to everyday life. The loss of smell or a decreased ability to smell affects approximately 1% of people under age 60 and more than half of the population beyond this age.

Abnormalities of olfaction include the following: (1) anosmia (absence of the sense of smell); (2) hyposmia (diminished olfactory sensitivity); (3) dysosmia (distorted sense of smell); (4) phantosmia (perception of an odorant when none is present); and (5) agnosia (inability to classify, contrast, or identify odor sensations verbally, even though the ability to distinguish between odorants may be normal).

Disorders of the sense of smell are caused by conditions that interfere with the access of the odorant to the olfactory neuroepithelium (transport loss), injure the receptor region (sensory loss), or damage the central olfactory pathways (neural loss). Table 10–1 summarizes the most common causes of olfactory dysfunction.

Table 10–1. Causes of Olfactory Dysfunction.

Classification

Transport Olfactory Loss

Transport olfactory loss can result from the following conditions: a swollen nasal mucous membrane in acute viral upper respiratory infections; bacterial rhinitis and sinusitis; allergic rhinitis; and structural changes in the nasal cavity (eg, deviations of the nasal septum, polyps, and neoplasms). It is also likely that abnormalities of mucus secretion, in which the olfactory cilia are immersed, could result in a loss of olfactory sensitivity.

Sensory Olfactory Loss

Sensory olfactory loss results from damage to the olfactory neuroepithelium by any of the following causes: viral infections, neoplasms, the inhalation of toxic chemicals, drugs that affect cell turnover, and radiation therapy to the head.

Neural Olfactory Loss

Neural olfactory loss can occur in a number of ways: head trauma, with or without fracture of the base of the anterior cranial fossa or cribriform plate area; Parkinson disease; Alzheimer disease; Korsakoff psychosis; vitamin B12 deficiency; neoplasms of the anterior cranial fossa; neurosurgical procedures; administration of ...

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