Chronic olfactory dysfunction, both hyposmia and parosmia, from the COVID-19 pandemic is a growing public health crisis with up to 1.2 million people in the United States affected. Olfactory dysfunction impacts one's quality of life significantly by decreasing the enjoyment of foods, creating environmental safety concerns, and affecting one's ability to perform certain jobs. Olfactory loss is also an independent predictor of anxiety, depression, and even mortality. Recent research by our group (unpublished data) and suggests that parosmias, moreso than hyposmias, can result in increased rates of anxiety, depression, and even suicidal ideation. While the pandemic has increased the interest by the scientific community in combating the burgeoning health crisis, few effective treatments currently exist for olfactory dysfunction. Persistent symptoms after an acute COVID-19 infection, or "Long COVID" symptoms, have been hypothesized to be a result of sympathetic positive feedback loops and dysautonomia. Stellate ganglion blocks have been proposed to treat this hyper-sympathetic activation by blocking the sympathetic neuronal firing and resetting the balance of the autonomic nervous system. Studies prior to the COVID-19 pandemic have supported a beneficial effect of stellate ganglion blocks on olfactory dysfunction, and recent news reports and a published case series have described a dramatic benefit in both olfactory function and other long COVID symptoms in patients receiving stellate ganglion blocks. A previous pilot study using stellate ganglion blocks of 20 participants with persistent COVID-19 olfactory dysfunction resulted modest improvements in subjective olfactory function, smell identification, and olfactory-specific quality-of-life, but it lacked a control group. Therefore, we propose a double-blinded, placebo-controlled randomized clinical trial assessing the efficacy of a stellate ganglion block versus saline injection in a total of up to 140 participants with persistent COVID-19-associated olfactory dysfunction.

One of the hallmark symptoms of infection with SARS-CoV-2 is olfactory dysfunction (OD). While the majority of patients recover from COVID dysosmia, up to 15%-25% have long-term hyposmia and it is estimated that up to 1.2 million people in the United States will experience chronic OD from the COVID-19 pandemic. A unique feature of COVID-19-associated OD is the high rate of persistent parosmia. In one study of 222 patients with COVID-19-associated olfactory dysfunction by Lerner et al, 148 (67%) of these patients experienced parosmia at some point, and estimates of persistent parosmia 6 months after COVID-19 infection range from 25% to 57%.Patients with OD have decreased quality-of-life and have described their lives as if "living in a box." These patients have concerns for environmental safety, decreased enjoyment of their food, depression, anxiety, and even a higher risk of mortality. Unpublished work by our group has demonstrated a relationship between parosmia and increased risk of screening positive for anxiety, depression, and suicidality.

The COVID-19 pandemic has highlighted the importance of the sense of olfaction, but no standard of care treatment for post-viral OD exists. The most commonly used treatment for post-viral OD is olfactory training; however, a large proportion of patients do not receive benefit and continue to have persistent symptoms. A multitude of other therapies have been tried in randomized clinical trials with minimal success, including theophylline, vitamin A, sodium citrate, and intranasal insulin. As a result, there is a critical need for the development of a novel intervention to address the large number of patients with OD due to the COVID-19 pandemic.

The stellate ganglion block (SGB) is proposed to inhibit the sympathetic neural connections within the head, neck, and upper extremity, improve regional blood flow, reduce adrenal hormone concentration, and even reestablish circadian rhythms through modulation of melatonin. The SGB has been used successfully in a multitude of disorders, including post-traumatic stress disorder, migraine, and complex regional pain syndrome. A meta-analysis of 12 clinical trials found that SGB was superior to placebo in reducing pain scores among patients with various sympathetic hyperactivity-associated disorders. Many "long COVID" symptoms, those that persist after recovery from acute COVID-19 infection, are hypothesized to be, at least in part, a result of sympathetic hyperactivity resulting in positive feedback loops. Therefore, the stellate ganglion block (SGB) is hypothesized to reset the balance of the autonomic nervous system and provide relief for long COVID symptoms, including OD.

The SGB was first proposed to treat OD by Lee et al in 2003, where 38 post-viral OD participants were treated with SGB and 13 participants remained untreated as controls. Subjective olfactory function improved in 27 (71%) of the treated participants compared to zero (0%) of the controls. Olfactory perception was improved significantly in the SGB group assessed both by the butanol threshold test and odor identification test. Additional studies by Moon et al noted improvement in OD of various etiologies after repeated SGBs. However, each of these studies were limited by their use of unvalidated outcome measures in a heterogeneous OD population in the pre-COVID era, limiting their external validity to the present day.

A multitude of anecdotal news reports and published case series point to a possible beneficial effect of the SGB on both chronic COVID-19-induced OD and various other long COVID symptoms. Numerous pain management clinics across the country are offering the SGB for long COVID with thousands of dollars of out-of-pocket costs to patients without adequate evidence to justify its use. One case series of 195 parosmic patients noted up to a 75% response rate after SGB.

Recently, our study team completed a prospective, pilot single-arm trial of 20 participants with persistent COVID-19-associated OD who underwent bilateral stellate ganglion blocks and were followed for 1 month post-procedure. At 1-month, 10 (50%) participants experienced at least slight subjective improvement in their OD, 11 (55%) attained a clinically meaningful improvement in smell identification using the UPSIT, and 7 (35%) achieved a clinically meaningful improvement in olfactory-specific QOL. Therefore, we propose a double-blinded, placebo-controlled randomized clinical trial assessing the efficacy of a stellate ganglion block versus saline injection in a total of 140 participants with persistent COVID-19-associated parosmia.

Inclusion Criteria:

1. Adults age 18 to 70
2. Diagnosis of COVID at least 6 months prior to study enrollment with self-reported parosmia
3. Ability to read, write, and understand English
4. Score of at least 40 on DiSODOR during screening and at least 25 during Visit 1

Exclusion Criteria:

1. History of smell loss or change prior to COVID-19 infection

2. History of conditions known to impact olfactory dysfunction

   1. Chronic rhinosinusitis
   2. History of prior sinonasal or skull base surgery
   3. Neurodegenerative disorders (Parkinson's disease, Huntington's disease, Amyotrophic Lateral Sclerosis, Lewy body dementia, frontotemporal dementia)

3. Currently using concomitant therapies specifically for the treatment of olfactory dysfunction

4. Inability to tolerate a needle injection into the neck

5. History of coexisting conditions that make SGB contraindicated:

   1. Unilateral vocal cord paralysis
   2. Severe COPD (FEV1 between 30-50% of predicted)
   3. Recent myocardial infarction within the last year
   4. Glaucoma
   5. Cardiac conduction block of any degree

6. Currently taking blood thinners or antiplatelet agents, including aspirin >81mg.

7. Allergy to local anesthetic

8. Inability to extend the neck for any reason (e.g., severe arthritis)

9. History of prior stellate ganglion block

Of 48 randomized participants,32 were randomized to SGB and 16 to placebo arm.

Adverse events will be recorded from the time of dose administration (the stellate ganglion block or placebo injection) through the post-dose period and up to the final follow-up visit at approximately 3 months after the injection. The study team will monitor and document all adverse events throughout this entire timeframe.

All AEs will be documented and assessed for their relatedness to the study medication. The study team will monitor AEs continuously, and once aware of an AE, it will be reported according to institutional guidelines. Serious Adverse Events (SAEs) or Unexpected Adverse Events will be investigated by the study monitoring board and reported to Washington University HRPO following required reporting procedures.

Limitations include lack of objective assessment for parosmia, which remains poorly defined in the literature.