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.