In this new blog category “From our community”, we want to address treatments that are being discussed controversially by people affected by Long COVID and health care professionals. In the Altea forum, in stories, and in discussions with people affected by Long COVID, we have seen a number of treatment suggestions that are not officially recommended (yet). To help judge the safety and effectiveness of these treatments, we are exploring the science behind them to find out what kind of evidence is available, whether or not the available data is reliable, and which risks might be associated with these treatments. Today, we’re starting with the stellate ganglion block as a means to alleviate Long COVID symptoms.
What is the stellate ganglion?
The stellate ganglion is a collection of nerves that is part of the sympathetic nervous system. The sympathetic nervous system plays a crucial role in the regulation of unconscious processes, e.g., heart rate, respiratory rate, or digestion. It also mediates physiological changes in the so called “fight or flight” response in stress situations.
In 80% of people, two nerve bundles in the upper chest (the inferior cervical and first thoracic sympathetic ganglions) are fused into one, the stellate ganglion. There is one stellate ganglion on the left and right side, respectively. The name (stellate ganglion) refers to its star-shaped appearance. An illustration of the shape and location is presented in the Figure below. The stellate ganglion provides nerve signals to the head, neck, arms, and parts of the thorax (upper chest).
Shape and location of the stellate ganglion (Source: https://www.advancedheadachecenter.com/stellate-ganglion-block).
How does the procedure work?
The exact procedure is described in this video by the BMJ Journal “Regional Anesthesiology and Acute Pain Medicine”. In short, an anesthetic is introduced at the level of the C6 vertebra, which lies above the stellate ganglion to reduce the risk of puncturing nerves and blood vessels close to the stellate ganglion. The injection is usually guided by ultrasound as shown in the picture below. Approximately 5-10 mL of the anesthetic are injected above the stellate ganglion, allowing the anesthetic to spread towards its target.
In most studies, the block was performed in the right-sided stellate ganglion. This may be because the right side of the brain is more involved in stress response or because the right side of the body might have a higher incidence of sympathetic predominance.
Most patients benefit from the right-sided block, however according to Dr. Sean Mulvaney, around 1 in 20 patients do only benefit from a left-sided block. Many patients who benefit from one side might also benefit from additionally blocking the other side.
However, if a block on both sides is intended, it should never be performed on both stellate ganglions on the same day! The anesthetic can cause a temporary paralysis of the vocal cords: if one side is paralyzed this results in a hoarse voice but if both sides are paralyzed patients might experience difficulties breathing.
Ultrasound image during a stellate ganglion block. The yellow arrow indicates the path of the injection needle; the pink star indicates the location of injection; the blue line indicates the prevertebral fascia; the red circle indicates the carotid artery; the green oval indicates the C6 nerve root; AS, anterior scalene; C6, C6 vertebra; LC, longus coli. Excerpt from the video: https://www.youtube.com/watch?v=B6ROeVFUJSY from the channel of the BMJ Journal Regional Anesthesiology and Acute Pain Medicine.
What are the potential beneficial effects of a stellate ganglion block?
A stellate ganglion block (SGB) is used for diagnostic purposes in the case of chronic neuropathic pain. The SGB allows to determine whether the pain is mediated by the sympathetic nervous system in which case pain should be relieved or reduced upon injection of the anesthetic.
Moreover, for chronic pain conditions, SGB can have a therapeutic effect. Researchers suggest that the positive feedback circuit of the sympathetic neurons is interrupted during the block, leading to a reset of the system and thereby a decrease of hyperexcitability of the sympathetic system. The pain relieve outlasts the immediate effect upon numbing the nerves by injection of an anesthetic (usually lasts a few hours)
Due to the role of the sympathetic nervous system in the “fight or flight” reaction, a potential benefit of SGBs was also indicated for the treatment of certain anxiety disorders. Available research concentrates on its implications for posttraumatic stress disorder (PTSD). While several case studies report a benefit, the results of two randomized controlled clinical trials are inconsistent. One trial reported a significant improvement in PTSD symptoms after SGB while the other trial did not.
What are the risks associated with SGB?
According to a 2019 review on the complications arising from SGB, the most common side effects are hoarseness and lightheadedness. Moreover, hypertension, brachial plexus block, dysphagia, and cough have been reported. Hoarseness may be accompanied by the feeling of a lump in the throat or difficulties swallowing.
Right after the infection, patients may experience soreness at the injection side, a drooping eyelid, bloodshot and/or watery eyes, a stuffed nose, or the feeling of warmth in their upper extremities (arms, hands). In fact, a temperature change (1-3 degrees) in the arms can be used to judge whether the procedure was successful.
Severe side effects are rare and mainly connected to complications during the procedure. They may include infection, bleeding from puncture of an artery or vein, nerve damage, pneumothorax (collapsing lung), thyroid injury, esophageal and tracheal puncture, or Horner’s syndrome, a syndrome characterized by a constricted pupil (miosis), drooping eyelid (ptosis), decreased sweating (anhidrosis), and an inset eyeball (enophthalmos).
Clinical evidence for the benefits of a stellate blockade is still limited beside it being used for almost a century.
Is there evidence that SGB can help Long COVID patients?
The clinical evidence for SGB in Long COVID patients is very limited. Few cases of individuals who have benefited from the treatment have been published, however, no larger controlled clinical trials are available.
A study analyzing symptom outcomes of 41 Long COVID patients has been published in august 2023 as a preprint (see infobox). The majority of participants in this study reported an improvement across all symptoms. However, there are several limitations to the study design:
- It has not been assessed to what extend symptoms had improved (answer possibilities were limited to “improved” or “not improved”)
- The time between the procedure and data collection varied from patient to patient, which may have an impact on the reported outcomes.
- Data was only gathered from participants willing to answer the questionnaire during a follow-up call.
- Results were not compared to a control group that has not received the treatment.
Due to these limitations, the positive outcomes of this study have to be viewed with caution.
A study from the US, published in May 2023, assessed the impact of SGB on the most common symptoms related to Long COVID in 195 participants. The most significant improvement was observed for symptoms related to smell and taste. Of note, this study also did not include a control group.
In conclusion, SGB is a well-known procedure which is usually not associated with severe side effects. However, it’s safety has not been thoroughly assessed in Long COVID patients. For patients suffering from post-exertional malaise (PEM) the procedure could lead to a severe crash. Some patients have reported to benefit from SGB, but no robust clinical evidence is available yet. If considered, the treatment should be carefully discussed and evaluated with a health care professional.