Sudden sensorineural hearing loss (SSNHL) is a common emergency in otolaryngological clinics [1]. Although spontaneous resolution has been reported to occur in 32% to 65% of cases [2-4], clinicians suspect based on their experience that these numbers might be overestimated [5]. Systemic steroid remains mainstay of treatment [6], with recovery rate reported as 61% in a hallmark study [7], and intratympanic steroid is often used as primary, or combination, or salvage therapy, with varying recovery rate [8-10]. Moreover, if treatments fail and hearing loss remains as a sequalae, SSNHL may cause significant depression and loss of quality of life [10]. While systemic and intratympanic administration of steroids has been proposed as the mainstay of treatment for patients without spontaneous resolution, the only approved option as a salvage is hyperbaric oxygen therapy (HBOT), which is expensive and less accessible to the patients [5]. Therefore, diversifying the available measures for salvage therapy in SSNHL patients who are refractory to steroids would be meaningful for individuals who are on the verge of complete hearing loss. In this case, we present a case of successful hearing recovery after stellate ganglion block (SGB) in an SSNHL patient who failed to respond to systemic steroid therapy and subsequent intratympanic steroid therapy. This is the first report of SGB used as a salvage therapy for refractory SSNHL.

A 36-years-old woman presented to our pain center complaining of incomplete recovery from hearing loss in the right ear. Her symptoms had started 9 days prior to her visit to our clinic, and the patient had been treated with high-dose oral steroid therapy with methylprednisolone 48 mg daily and intratympanic dexamethasone every other day for 7 days at a local ear, nose, and throat (ENT) clinic.

Her initial audiogram demonstrated that her right ear had an air conduction threshold of 45-65 dB and a bone conduction threshold of 80-50 dB, while the air and bone conduction thresholds of her left ear remained normal (Fig. 1A).

Figure 1. The patient’s audiogram. (A) Initial audiogram from other hospital with increased hearing threshold in both bone and air conduction at right ear indicating SSNHL. (B) The patient’s audiogram after 3 sessions of SGB with decreased hearing threshold indicating complete recovery. Means of thresholds at 6 frequencies are lower than 25 dB. (C) The patient’s audiogram 4 weeks after completion of SGB. Hearing threshold remained in normal range. O: Right ear air conduction; X: Left ear air condoction; [: Right ear bone conduction masked; ]: Left ear bone conduction masked; Δ: Right ear air conduction masked.

We performed three sessions of right-sided SGB at 2-week intervals under ultrasound guidance (Fig. 2). We injected 5ml of 0.4 % lidocaine at prevertebral fascia at 7th level of spine. After 2 sessions of SGB, the patient experienced subjective recovery from hearing loss, and complete recovery was confirmed by an audiogram showing complete resolution after the 3rd session of SGB. Both the air and bone conduction thresholds were less than 15 db (Fig. 1B,C). This case report is approved by Institutional Review Board The Catholic University of Korea, Seoul St. Mary’s Hospital (IRB no : KC22ZISI0727), and written and informed consent was obtained from the patient.

Figure 2. Performing ultrasound guided right-sided stellate ganglion block. (A) Needle placed at between carotid artery and longus colli muscle. (B) After injecting local anesthetics, injectate is spread in between prevertebral fascia. SCM: Sternocleidomastoid muscle; CA: carotid artery; LC: longus colli muscle; TP: transverse process. Internal jugular vein is collapsed by pressure on ultrasound transducer.

This case is the first report of SGB used as a salvage therapy for an SSNHL patient who was refractory to systematic and intratympanic steroid therapy. Although the effect of SGB on SSNHL as part of a combination therapy is well researched [11-13], the effectiveness of SGB as a salvage therapy has not yet been investigated. In a previous study, improve of SSNHL after SGB was associated with early onset of treatment [11].

HBOT is an established salvage therapy for SSNHL [5]. However, possible complications, such as pulmonary and middle ear barotrauma and oxygen toxicity, and out of accessibility to centers applying HBOT are limitations of this treatment [14]. SGB could be an alternative salvage therapy method for SSNHL patients who are not eligible for HBOT.

The pathogenesis of SSNHL is still not well defined, but oxidative stress has been proposed as a possible mechanism [15]. The mechanism of SGB in SSNHL patients is speculated to be improvement of inner ear circulation [12], similar to other applications of nerve blocks in orofacial regions, for example, to treat anosmia or laryngopharyngeal reflux disease [16,17]. The effect of SGB is mediated by sympathetic blockade of the cervical region. Therefore, SGB must be performed correctly in order to treat SSNHL effectively. The stellate ganglion is located at the C7-T1 level, and the correct spread of the injectate depends on the correct placement of the needle tip between the prevertebral fascia and the longus colli muscle [18]. Ever since SGB has been performed for hearing loss patients [11-12,19], and the amount of anesthetics researchers used for SGB varied, from 3-5 ml to 7 ml. In this study, the author used 5ml of lidocaine. The correct placement of needle in the prevertebral fascia lets clinician to minimize the volume of injectate. The methodology for SGB has evolved from landmark-based to fluoroscopy-based to ultrasound-based methods. The ultrasound-guided method guarantees the most accurate placement of the needle tip, allowing direct visualization of the cervical level of the spine and associated structures, such as the carotid vessels, cervical muscles and associated fascial structures.

Therefore, the authors suggest that a sonography-guided procedure would be the most suitable method of SGB for patients with SSNHL. Adequate vasodilation can be achieved by precise blockade of the cervical sympathetic ganglia and gives rise to the therapeutic effect of SGB on SSNHL. Ultrasound-guided SGB could be an alternative salvage therapy for patients with refractory SSNHL. Currently, the authors are conducting a prospective study of SGB as a salvage therapy for SSNHL.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sector.

No potential conflict of interest relevant to this article was reported.