Post-infectious olfactory loss: a cohort study and update.

Post-infectious olfactory loss is defined as an olfactory dysfunction in the course of an upper respiratory tract infection. Quantitative olfactory dysfunction is usually moderate to severe, with many patients experiencing a qualitative disorder such as parosmia. Diagnosis is made on the basis of patient history, normal clinical examination (no inflammatory disease in the olfactory cleft) and decreased olfactory function. This paper provides an update of pathophysiology, clinical management and prognosis, and also looks at the clinical characteristic of a cohort of 122 patients from our department. Results from orthonasal and retronasal testing, chemosensory event-related potentials and olfactory bulb volume confirmed previous findings: our post-infectious olfactory patients were middle-aged women (sex ratio 2.4; mean age 53.9), with 47.5% and 18% of them complaining of parosmia and phantosmia respectively. More of them were hyposmic than anosmic (64.7% and 35.3% respectively) and 18 suffered repeat episodes. Olfactory bulb volume was correlated to psychophysical olfactory testing and orthonasal to retronasal scores. Olfactory-event-related potentials were found in about one-third of the patients and the vast majority of them had reproducible intranasal trigeminal event-related potentials. As there is no proven medical therapy for this disease, complete clinical evaluation of the patients may help to counsel patients about the recovery prognosis that applies to one-third of them.

Olfactory testing in clinical practice.

Numerous techniques are available in the clinic for the investigation of chemosensory function. Psychophysical testing using orthonasal and retronasal stimulation routes may help to distinguish anosmic from hyposmic patients. These psychophysical tests are most frequently used for odour identification and odour threshold. Chemosensory event-related potentials using olfactory and trigeminal stimulation have become part of the routine investigation of patients with olfactory loss in specialised smell and taste centres. The interpretation of results from psychophysical testing is frequently supported by the assessment of chemosensory event-related potentials. This review will discuss these methods, including how to perform them, focusing on normative data and describing some clinical examples from our centre (olfactory and trigeminal event-related potentials).