Olfaction means the chemoreceptive sense of smell and its disorder is called olfactory dysfunction. It is classified as quantitative and qualitative olfactory disorders. The former includes hyposmia and anosmia and the latter includes dysosmia, olfactory blindness, hyperosmia and so on. Olfactory dysfunction is also divided into respiratory, olfactory mucosa-related, combined (respiratory and olfactory mucosa-related), peripheral and central disorders based on anatomical locations that are responsible for the dysfunction. Major causal diseases are the chronic sinusitis, upper respiratory tract viral infection and head trauma. The prevalence of olfactory dysfunction is reported to be 1-3% of the US population while it has not been surveyed in Japan.
Many patients who experience olfactory symptoms undergo examinations by otorhinolaryngologists, who conduct the following procedures: interview, visual inspection, imaging examinations, and an olfactory function test. Accurate diagnosis and appropriate treatment of olfactory disorders require comprehensive assessment of the results of the above procedures, identification of the cause and site of origin, and evaluation of the severity of the disorder. This paper details the examinations used for diagnosing olfactory disorders and focuses on olfactory tests such as T&T olfactometer and intravenous olfaction test.
Chronic rhinosinusitis (CRS) is the most common pathogenesis of olfactory dysfunction. Of 60-80% in patients with CRS suffer from olfactory dysfunction. The olfactory dysfunction is considered as transport and/or sensory disorder. The olfactory dysfunction due to CRS is diagnosed by taking the past history, nasal endoscopic findings, radiological imaging (CT, MRI), and olfaction tests. Eosinophilic CRS (ECRS), increasing recently, appears the olfactory dysfunction at the earlier stage. Many cases in olfactory dysfunction due to ECRS are intractable. For the treatment, conservative treatment with nasal irrigation, medicines of corticosteroids and macrolide antibiotics and endoscopic sinus surgery (ESS) were selected by a combination.
Postviral olfactory disorder (PVOD) is one of the most common causes of persistent olfactory loss. It predominantly affects middle-aged and elder women. The patients usually notice loss of smell while they have a cold, but visit ENT clinics only after several weeks/months, realizing that the olfactory impairment persists despite the resolution of cold symptoms. The pathophysiology of PVOD is thought to be sensorineural damage of the neuroepithelium and/or central olfactory tracts, either by direct viral insult or by immune reaction against the virus. Endoscopic and radiological examinations reveal no abnormalities, and are useful to differentiate PVOD from other causes of olfactory impairment. Zinc, Kampo medicines, steroids, vitamins, and cerebral metabolic activators have been used singly or in combination for the treatment of PVOD. Recent studies have also reported the usefulness of olfactory training for the treatment of PVOD. Relatively long periods (>1 year) are usually necessary for the significant improvement of olfactory function.
SPECT-MRI thallium olfacto-scintigraphy (SMT olfactoscintigraphy) with nasal administration of thallium-201 (201Tl) has been developed to determine the lesion of post-traumatic olfactory nerve damage. Disconnectivity of olfactory nerve assessed with SMT olfactoscintigraphy was significantly correlated with the reduced olfactory bulb volume. The migration of nasally administered 201Tl to the olfactory bulb was also significantly correlated with the olfactory bulb weight in the mice. The clinical outcome of the treatment with Kampo medicine in the patients with post-traumatic olfactory impairments was shown.
54-67% of patient with allergic rhinitis has olfactory dysfunction (anosmia, hyposmia). 21-45% of them also significantly decreases the olfactory threshold. Causes of olfactory disturbance are rhinosinusitis, sequel of cold, head injury and allergic rhinitis in decreasing order. Olfactory dysfunction due to allergic rhinitis is thought to respiratory disorder. They might be treating as at least both moderate and nose closed type by usual Japanese allergic rhinitis guideline. It is thought to be a relatively good prognosis and a pathological condition that can be improved by appropriate treatment.
The sense of smell decreases rapidly after the age of 60 years and over, and by age 80, the sense of smell is reduced by about half. A reduced sense of smell affects quality of life such as the flavor of foods and beverages, and It is especially important for the elderly impaired immune defense to perceive the sense of smell.
Congenital anosmia is an infrequent phenomenon. Two broad categories are often considered : isolated congenital anosmia and congenital anosmia with other anomalies. The most commonly described association is that of anosmia or hyposmia with hypogonadotropic hypogonadism, also called Kallmann syndrome. MRI (magnetic resonance imaging) is useful for the detection of the morphologic abnormalities of patients with congenital anosmia. Patients with congenital anosmia should understand handicaps associated with anosmia, and it is neccesory to have a detailed examination of hypogonadism.