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Causes of Anosmia, Hyposmia, Cacosmia, Parosmia & Hyperosmia

Definition: Anosmia is complete loss of sense of small, while hyposmia is diminished sense of smell.

Causes of Anosmia and Hyposmia

Nasal:

I. Obstruction: the small particles do not reach the olfactory mucosa e.g. Deviated septum, nasal polyps and nasal synechiae.
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II. Misdirection of air current (disruption of nasal aerodynamics or turbulence):
  • Destruction of alae nasi e.g. granulomas and tumors.
  • Aggressive removal of turbinates.

Mucous membrane changes:

  • In allergic rhinitis there is excess secretions which wash out the small particles.
  • In atrophic rhinitis, the mucus is too thick to dissolve the smell particles.

Interference with nerve endings:

  • Degeneration of nerve endings as in atrophic rhinitis.
  • Post infleunza neuritis of olfactory nerve endings.
  • Diabetic neuritis
  • Lead poisoning.

Intracranial:

  • Congenital absence of olfactory bulbs and nerves.(rare)
  • Fracture base of skull involving the anterior cranial fossa.
  • Basal meningitis.
  • Tumors of anterior cranial fossa e.g.: meningioma and neuroblastoma leading to compression of olfactory pathway.

Psychogenic:

Malingering: The patient will deny smell of any odor even irritant odors which stimulate trigeminal nerve (ammonia).
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Tests of smell:

  • Subjective: Measuring the minimum perceptible odor, Identification test.
  • Objective: Olfactory evoked response.

Cacosmia:

Definition: Bad odor perceived by patient and sometimes his contacts.
Causes:
  • Neglected foreign body in the nose.
  • Atrophic rhinitis.
  • Maxillary sinusitis especially of dental origin.

Parosmia (Hallucination of smell):

Abnormal sense of smell which is perceived by patient alone, this disorder is found in many psychiatric disorders as schizophrenia and depression.

Hyperosmia:

Increased sense of small, it is met in some psychiatric diseases or irritative lesions of olfactory bulb. It may also lead to migraine (migraine related hyposmia).

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