Anosmia

Authors

Affiliations

Nate Yomogida, B.S., SPT

Doctor of Physical Therapy

B.S. in Kinesiology

Chloë Kerstein, B.S., SPT

Doctor of Physical Therapy

B.A. in Neuroscience

Anosmia refers to olfactory (smell) loss and can be unilateral or bilateral¹.

Testing

Testing Unilateral Anosmia

• Unilateral anosmia is difficult to diagnose since it is a sympton, not a sign, and patients rarely notice this change since the contralateral nostril can compensate¹.
• To avoid contralateral nostrile compensation, the examiner must test each nostril separately¹.

Bilateral Anosmia

• Most patients are aware of bilateral anosmia and may even report decreased taste due to olfaction’s contriution to the perception of flavor¹.

Possible Causes of Anosmia

• Head trauma
• Viral infection
• Nasal obstruction
• Neurodegenerative conditions
• Frontal lobe lesions

Head Trauma

• Trauma to the head can cause anosmia by damaging the olfactory nerves as they penetrate the cribriform plate of the ethmoid¹.

Viral infection

• Viral infections can damage the olfactory neuroepithelium¹.
• Examples include:
  • Covid-19¹

Obstruction

• Obstruction of the nasal passages can impair olfaction¹.

Neurodegenerative Conditions

• Bilateral anosmia is also seen in Kallmann syndrome (anosmic hypogonadism)¹
• Parkinson’s disease¹
• Alzheimer’s disease¹

Frontal lobe Lesions

• Intracranial lesions that occur at the base of the frontal lobes near the olfactory sulci can interfere with olfaction¹.
  • Possible lesions in this location include meningioma, metastases, basal meningitis, or less commonly sarcoidosis, a granulomatous inflammatory disorder that occasionally involves the nervous system, often causing cranial neuropathies¹.
• Frontal lobe deficits are often difficult to detect clinically, especially with small lesions¹.
• As a result, lesions at the base of the frontal lobes can sometimes grow very large while still causing little symptoms except besides anosmia.
• Large lesions of the olfactory sulcus region, especially meningiomas, can cause Foster Kennedy syndrome where the patient experiences anosmia, ipsilateral optic atrophy (d/t tumor compression), and contralateral papilledema (d/t elevated intracranial pressure)¹.

References

1.

Blumenfeld H. Neuroanatomy Through Clinical Cases. 3rd ed. Oxford university press; 2022.