Olfactory Recovery Is Possible Following Post-Infectious Olfactory Loss

What are the significant predictors for olfactory recovery in a large sample of patients with postinfectious olfactory loss (POL) using standardized objective testing methods?

Bottom line
Olfactory recovery occurs many years after the viral event, meaning a good prognosis for postinfectious olfactory loss patients, especially for those with initially poor olfactory function and younger age.

Background: POL is among the most common causes of olfactory impairment, creating substantial negative impact on patients’ quality of life. It has been estimated that about one-third of patients may experience spontaneous recovery, usually within two to three years after the infectious event, but most studies are based on small sample sizes, assessed in the short term, and use different testing procedures.

Study design: Retrospective cohort analysis of 791 patients with POL.

Setting: Interdisciplinary Centre for Smell and Taste of the Technical University of Dresden, Germany.

Synopsis: Patients were tested on two occasions (T1 and T2), with a follow-up variation in time ranging from 13 to 4,251 days. At the first visit, 39.6% of patients were diagnosed as anosmic, 57.9% as hyposmic, and 2.5% as normosmic. No differences were observed between males and females in age, TDI score (odor threshold (T), discrimination (D), and identification (I)), or in threshold and identification measurements, although females outperformed males in odor discrimination. Age correlated weakly, but significantly with the TDI score, discrimination, and identification, but not with thresholds.

Baseline TDI score and patient age at T1 were the only significant predictors of patients’ delta TDI (higher TDI score and higher age = lower delta TDI scores). All decades of age showed delta TDI improvement (ages 15-30: 80.0%; ages 31-40: 83.9%; ages 41 to 50: 89.4%; ages 51 to 60: 82.9%; ages 61 to 70: 81.5%; ages 71 to 85: 77.1%). Patients whose olfactory acuity worsened had initially higher TDI scores; those who clinically improved had the lowest initial scores. Increasing age at T1 was related to a worse olfactory diagnosis at T2, but higher baseline TDI scores were related to a better diagnosis outcome at T2. Limitations included a high proportion of patients with more long-standing dysfunctions, and potential bias due to recall errors.

Citation: Cavazzana A, Larsson M, Münch M, Hähner A, Hummel T. Postinfectious olfactory loss: A retrospective study on 791 patients. Laryngoscope. 2018;128:10–15.