Follow-up and Outcomes
Two months after the first visit, the threshold of the skin of the right upper lip and the right lateral nasal wing was 0.02 g according to the SWMT. After six sessions of SGB, the healthy contralateral areas showed an improvement in the upper lip and lateral nasal wing of 0.014 g and 0.008 g, respectively. After eight sessions of SGB, numbness improved, as a subjective symptom. Since discomfort during eating disappeared, the treatment was terminated. HADS-A remained unchanged at 9 points. HADS-D decreased to 3 points.
DISCUSSION
By temporarily blocking the sympathetic nervous system, SGB causes dilation of the internal carotid and vertebral arteries, which run through the brain and spinal cord. The resulting increase in blood flow not only improves pain associated with local circulatory disturbances (ischemia), but also has a positive effect on hypothalamic function, thereby promoting neural recovery. SGB is used for treatment of migraine, upper limb pain, and atypical facial pain.3Since SGB is used for treatment of many systemic diseases, including those of the immune and endocrine systems, it has a wider range of indications in Japan than in Europe or the United States.4
Trigeminal neuropathy is a general term for a condition in which the trigeminal nerve becomes dysfunctional due to trauma, tumors, infectious or demyelinating diseases. Trigeminal neuropathy results in sensory abnormalities, with or without pain.5 In the present case, there was no pain at the time of initial examination. However, sensory abnormalities were observed, leading to a diagnosis of trigeminal neuropathy.
Although there is no established treatment of unexplained paraesthesia and numbness, SGB was effective in this case in which SWMT showed improvement in the threshold. There are a few reports on the treatment of unexplained paraesthesia. The mechanism of the therapeutic effect of SGB in this case may be similar to that of SGB on complex regional pain syndrome and post-traumatic stress disorder. Nerve growth factor (NGF) increases in response to acute or chronic stress. It promotes growth of the sympathetic nerve endings and increases noradrenaline levels in the brain. SGB exerts a therapeutic effect by reducing the levels of NGF and noradrenaline.3,6 Acupuncture treatment could alter the secretion patterns of noradrenaline, gamma aminobutyric acid, and serotonin.6 Furthermore, increased sympathetic tone could reduce the function and sensitivity of pinealocytes, attenuating melatonin rhythms and causing various diseases. However, the mechanism of action of SGB comprises sympathetic inhibition within the innervated area, causing vasodilation. This not only increases blood flow, but also triggers restoration of melatonin secretion by the pineal gland, normalizing the physiological melatonin rhythms.4Regarding treatment of stress-related illnesses, mindfulness may be effective in reducing stress by decreasing sympathetic activity and increasing parasympathetic activity.7 SGB induces a parasympathetic-dominant state, which is characterised by peripheral blood vessel dilation, increases in blood flow and respiratory rate, and a decrease in heart rate. In the present case, deep sleep and reduced heart rate were also observed after each SGB session, indicating a relaxing effect due to sympathetic suppression.
In this case, although there was no apparent aetiology of numbness, there was a change in the work environment due to the COVID-19 pandemic restrictions. The onset of numbness occurred in a more stressful situation than before. The post-SGB HADS assessment showed improvement in the depression rating scale. In addition, numbness could be a symptom of somatisation disorder or depression.8 Therefore, it is possible that numbness in this case may have developed due to psychological factors.
CONCLUSION
A decrease in heart rate and deep sleep after SGB showed a relaxing effect due to sympathetic suppression and an improvement in depression rating scale. These results suggest that SGB might be effective in the treatment of facial numbness related to mental stress.