Stellate Ganglion Block for the Treatment of COVID-19-Induced Parosmia: A Randomized Clinical Trial.

IMPORTANCE

Smell distortion (parosmia) is a symptom of post-COVID-19 condition that persists and has immeasurable detriments on quality of life. To date, a standard criterion for treatment of this bothersome condition has not been identified.

OBJECTIVE

To determine whether stellate ganglion block (SGB) is effective and safe in improving olfactory dysfunction in patients with persistent COVID-19-induced parosmia.

DESIGN, SETTING, AND

PARTICIPANTS

This was a randomized, double-blinded, placebo-controlled clinical trial conducted from October 2023 to September 2024 at a single center study (the Washington University in St Louis/Barnes Jewish Hospital). A volunteer sample of 192 individuals were screened; 57 were enrolled after meeting eligibility criteria (age 18-70 years with self-reported parosmia of ≥6 months since COVID-19 infection, and a screening score of ≥40 on the Parosmia Olfactory Dysfunction Outcomes Rating [DisODOR] scale). Of 135 excluded, the most common reasons were prior SGB (n = 42) and parosmia resolution or non-COVID-19-induced parosmia (n = 28). Data were analyzed from September to October 2024.

INTERVENTION: Ultrasonography-guided injection of 6 to 8 mL of active mepivacaine, 1%, or saline, 0.9%, at the right or left (randomized 1:1) stellate ganglion was performed by a board-certified anesthesiologist and pain medicine specialist.

MAIN OUTCOME AND MEASURE: Between-subject difference of 25% in proportion of responders (defined by a 15-point decrease in DisODOR score) from baseline.

RESULTS

The study evaluated 48 participants, 32 randomized to SGB (median [range] age, 45 [19-64] y; 25 [81%] female), and 16 to placebo (median [SD] age, 45 [26-64] y; 13 [81%] female). Time since COVID-19 infection was similar between groups (SGB, 35.3 vs placebo, 30.6 months; MD = -3.1 months; 95% CI, -10.9 to 3.7). Three-month response rate was 43% (n = 13) for SGB and 38% (n = 6) for placebo (difference, -5%; 95% CI, -32% to 33%). There was no between-group difference in clinical global impression of improvement.

CONCLUSIONS AND RELEVANCE: This randomized clinical trial found that SGB is not superior to placebo in treating COVID-19-induced parosmia, and thus, should not be recommended as treatment.

TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT06253806.