Definition: Anosmia is complete loss of sense of small, while hyposmia is diminished sense of smell.
Causes of Anosmia and Hyposmia
I. Obstruction: the small particles do not reach the olfactory mucosa e.g. Deviated septum, nasal polyps and nasal synechiae.
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.
- 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.
Malingering: The patient will deny smell of any odor even irritant odors which stimulate trigeminal nerve (ammonia).
Tests of smell:
- Subjective: Measuring the minimum perceptible odor, Identification test.
- Objective: Olfactory evoked response.
Definition: Bad odor perceived by patient and sometimes his contacts.
- 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.
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).