Workup and Therapeutic Options
A detailed history should include the duration and degree of olfactory loss and an inquiry in the status of chemosensory ability prior to the present complaint of olfactory dysfunction. Patients may present with taste alteration, but may be experiencing decreased flavor due to an olfactory disorder with the preservation of taste perceptions of sweet, bitter, sour, and salt. True gustatory loss is much less common than olfactory loss. Events occurring around the time of the noticed loss of olfactory ability may include URI, head injury, toxin or fume exposure, or surgery. In patients with a fluctuating smell ability or a gradual onset of dysfunction, rhinosinusitis or polyps may be the cause and nasal symptoms should be assessed. Patients should provide examples of what they can smell or should attempt to describe the odors they perceive with dysosmias. For patients with phantosmia, there may be a history of triggers or periods during the day when the smell is not present. Other pertinent history includes epistaxis or nasal airway obstruction, CNS complaints, endocrine abnormalities, occupational or tobacco exposure, or a history of neurodegenerative disorders in the patient or in the family history, as well as a review of medications.
Physical exam should consist of a complete ear, nose, and throat examination with an emphasis on nasal airway evaluation. Nasal endoscopy is warranted for the evaluation of nasal airflow obstruction blocking access to the olfactory cleft from septal deviation or polyps, the presence of tumors, mucosal edema or postoperative changes, crusting, or scarring. For patients with parosmia or phantosmia localized to one nostril, blocking that nostril to airflow may change the patient′s perception of the abnormal smell. Cranial nerve function should be assessed as well as an evaluation of mental status for AD or motor function for PD.
Computed tomography (CT) scans of the nasal cavity, paranasal sinuses, and anterior skull base may be indicated in the evaluation of olfactory disorders when the symptoms or olfactory tests do not fit a particular diagnosis. Coronal scans can evaluate the patency of the olfactory cleft and can help to rule out tumors or deformities in the anterior cranial fossa. MRI can further evaluate the extent of soft tissue masses or aid in the evaluation of the CNS, including olfactory tracts and olfactory bulbs ( Fig. 4.3 ). Olfactory bulbs are absent in anosmia with Kallmann syndrome ( Fig. 4.4 ), and bulbs may have decreased volume in patients with trauma-induced anosmia or olfactory disorders with schizophrenia.29,71
An assessment of olfactory ability is necessary for establishing the degree of olfactory loss and allows for objective monitoring of changes in olfactory ability over time. In addition, testing may help detect malingerers or establish compensation for permanent disability. Psychophysical tests include self-administered tests that are clinically useful in the diagnosis of olfactory disorders and are widely commercially available. Smell identification tests require the patient to smell an odorant and choose the correct name from a multiple-choice test. One such test is the Smell Identification Test (SIT, also known as the University of Pennsylvania Smell Identification Test or UPSIT) that was noted previously, which includes 40 “scratch and sniff” odorants with four possible answers and is self- administered. Norms have been established by age and gender and have been classified as normosmia, microsomia, or anosmia, with scores below 5 to 6 suggesting malingering (as 10 out of 40 is considered chance performance).72 The Cross- Cultural Smell Identification Test (CC-SIT), also known as the Brief Smell Identification Test (B-SIT), is a 12-item version of the SIT, which includes odors most consistently identified by subjects in various countries and is a useful screening tool for more rapid screening.73 The “Sniffin’ Sticks” test incorporates odor threshold or the lowest concentration of detectable odorants, odor discrimination or ability to correctly choose a target odorant, and odor identification using multiple choices for a combination score for threshold, discrimination, and identification (TDI). Normative data have also been established for normal and affected patients based on TDI scores.74 These tests can be administered bilaterally or unilaterally by occluding one nostril to assess for laterality of olfactory deficits when appropriate.
Electrophysiological tests are available but are primarily used for research purposes. Odor event-related potentials measure brain-evoked potentials from electroencephalograms averaged after multiple exposures to an odorant.75 Another procedure is the electro-olfactogram, which involves placing an electrode directly on the olfactory epithelium. A slow-negative shift in voltage is detected with the introduction of an odorant to stimulate the olfactory receptor neurons. The placement of these electrodes can be unpleasant for the patient and can be technically difficult in the endoscopic manipulation of the electrode and an inability to confirm placement in the olfactory rather than the respiratory epithelium.76 Recent studies have found preliminary evidence of an intrinsic optical signal, which is visible using 600 to 700 nm wavelength light when the olfactory epithelium is stimulated by odorants. This may be useful for evaluating the function of a region of the epithelium rather than one isolated spot as is measured with an electrode in an electro-olfactogram.77