Case Reports Recurrent Laryngeal Nerve Afferents and Their Rake in Laryngospasm Joel A. Sercarz, MD, Sina Nasri, MD, Bruce R. Gerratt, Ph.D, Steven T. Fyfe, MD, and Gerald S. Berke, MD Airway protection is a critical and phyloge- the basis of this clinical report. In both pa- neticaly old function of the larynx. Therefore, tients, laryngeal surgery for vocal fold medi- the sensory supply to the larynx is extensive, alization was performed and was complicated including afferent nerve endings in the mu- by postoperative laryngospasm, which re- cosa, muscles, and joints. The majority of af- solved after the injection of the ipsilateral ferent fibers are in the distribution of superior RLN with lidocaine. laryngeal nerve (SLN). The afferents of the re- current laryngeal nerve (RLN) have been in- CASE REPORTS frequently studied in humans. Laryngospasm is defined as a prolonged oc- Case 1 clusion of the glottis caused by contraction of The patient is a 61-year-old woman who pre- the intrinsic laryngeal muscles. It is a well- sented with a g-year history of dysphonia caused known potential hazard of any type of laryn- by an idiopathic left true vocal cord paralysis. Her geal or pharyngeal surgery. Laryngospasm is previous evaluation included a computed tomogra- more likely in the presence of excessive secre- phy (CT) scan from the skull base to the mediasti- tions or in patients who are extubated in an num and a barium swallow, both of which were normal. She complained of breathy vocal quality inappropriate plane of anesthesia. Laryngo- and lack of vocal strength. She denied a history of spasm has been observed in 0.87% of all pa- laryngeal trauma, aspiration, dysphagia, thyroid tients undergoing general anesthesia, and in surgery, neck mass, odynophagia, smoking, or al- 1.74% of children 0 to 9 years of age.’ Laryn- cohol use. Her past history was significant for gospasm is more common when the larynx is asthma. instrumented during a procedure. On examination, the voice was breathy and hoarse. Laryngostroboscopy showed incomplete Laryngospasm can be differentiated from re- glottal closure, diminished excursion of the left vo- flex laryngeal closure, which is shorter in du- cal fold, and absence of a left mucosal wave. This ration, and can be elicited by a wider variety was consistent with an idiopathic left recurrent la- of stimuli. According to Suzuki and Sasaki,’ ryngeal nerve paralysis. The patient was admitted in July 1990 for a left- laryngospasm is elicited only by repetitive su- sided arytenoid adduction. The procedure was un- prathreshold stimulation of SLN afferents. complicated, but in the recovery room shortly We recently obtained evidence for the pres- thereafter, she developed intractable laryngo- ence of RLN afferents and showed their pos- spasm. Her arterial oxygen saturation decreased to sible role in laryngospasm. Two cases form 80%. The laryngospasm and airway distress were per- sistent and an emergency tracheostomy was re- From the Division of Head and Neck Surgery, UCLA quired. After the tracheostomy, the larynx was School of Medicine, Los Angeles, CA; and the VA Med- video recorded, showing continued laryngospasm. ical Center, West Los Angeles, CA. Address reprint requests to Joel A. Sercarz, MD, Divi- The RLN was injected in the tracheoesophageal sion of Head and Neck Surgery, Center for the Health groove on the operated (left) side, 1 cm inferior to Sciences, 10833 Le Conte Ave, Los Angeles, CA 90024. the cricoid cartilage. The laryngospasm was broken Copyright 0 1994 by W.S. Saunders Company after the injection; the findings were recorded on a 0198-0709/94/l 508-0008$5.00/O videotape (Figs 1 and 2). The patient tolerated American Journal of Otolaryngology, Vol 18, No 1 (January-February), 1995: pp 49-52 49 50 SERCARZ ET AL Fig. 1. Photograph of larynx (case no. 1) after arytenoid adduction laryngoplssty showing laryngospasm. plugging of the tracheostomy tube, and has not had DISCUSSION a recurrence of laryngospasm after decannulation. Although the human RLN is known to have Case 2 afferent fibers, they have been studied primar- ily in laboratory animals. Basic research in the The patient was a 38-year-old man when he first cat model documented the presence of RLN presented to UCLA in 1987 for the evaluation of sensory fibers in the infraglottic larynx similar hoarseness. He was found to have a T, squamous- to the SLN fibers in the supraglottis. Signifi- cell carcinoma of the left larynx. He underwent ver- cantly, research by Kirchner and Wyke3-6 in tical partial laryngectomy in February, 1987. The pathological analysis indicated that the surgical the 1960s showed that the RLN has afferent margins were free of tumor. innervation of the laryngeal joints. The affer- After surgery, the patient developed a breathy ent fibers played a role in laryngeal closure dysphonia that reduced his ability to generate ad- when electrically stimulated. equate vocal strength. Videolaryngoscopy showed The airway has numerous receptors in- an adequate airway but significant glottic chink with inadequate projection of the pseudocord. volved with airway protection and reflex la- Therefore, he underwent transcutaneous Teflon ryngeal closure. These include chemorecep- (Polytef, Mentor Inc., Norwell, MA) injection of the tors, which are involved in laryngeal protec- pseudocord in March 1988. tion and the laryngeal chemoreflex: if water is He continued to have a breathy voice despite the placed into the larynx, then apnea, swallow- augmentation, so a second transcutaneous injec- tion was performed in August 1990. Immediately ing, and cardiovascular changes occur.7 Re- after the operation, he developed severe airway dis- ceptors in the larynx are also responsible for tress. Indirect laryngoscopy showed laryngospasm. proprioception, pressure, tactile, and sensitiv- He received 8 mg of dexamethasone and an injec- ity to water and many chemical stimuli. In tion of 1% lidocaine to the left RLN. This strategy addition, there are mechanoreceptors in the was used because of its success with the patient described in case no. 1. The patient’s laryngospasm laryngeal muscles and joints that also have was broken and his airway distress resolved with- significant influence on laryngeal reflexes. out further intervention. Attempts to arrest laryngospasm experi- LARYNGEAL AFFERENTS AND LARYNGOSPASM 51 In both of the clinical cases presented, laryngospasm occurred after a laryngeal pro- cedure and was arrested by lidocaine injec- tion of the RLN on the side of the surgery. The effectiveness of this treatment is unexpected in case no. 1, because the efferent fibers of the RLN were paralyzed. Nonetheless, it is likely that afferent nerve fibers in the RLN were re- sponsible for the reflex laryngospasm. One possibility is that mechanoreceptors in the cricothyroid joint could have produced the af- ferent stimulus for the reflex spasm of the con- tralateral cord. The vagus nerve was most likely not injected, given the technique used Fig. 2. Photograph of larynx (case no. 1) after injection on for administration. In case no. 2, the injection 1% lidocaine hydrochloride into the left RLN, showing cessation effectively arrested the laryngospasm, despite of the laryngospasm. resection of some of the laryngeal muscula- ture and the mucosa on the side of the injec- mentally have included electrical stimulation tion of the PCA muscle to promote abduction.’ These cases suggest that RLN afferents, in Other investigators have attempted to prevent addition to the more commonly implicated laryngospasm with topical lidocaine placed SLN afferents, may be responsible for laryn- into the airway.g In the experimental setting, gospasm in the human. The musculature in- laryngospasm has been blocked in canines volved in laryngospasm may be either ipsilat- with blocking electrodes.” No previous at- era1 or contralateral to the stimulus. Finally, tempt to arrest laryngospasm with lidocaine the RLN afferents may persist despite idio- injection has been reported. pathic laryngeal paralysis or resection of a A canine study by Sant’ambrogio et al’* dis- portion of the larynx, as with vertical partial covered that the abundant receptors for tem- laryngectomy. perature in the supraglottis (SLN) are not In the majority of cases, laryngospasm is present in the area supplied by the RLN, a most likely caused by SLN afferents. How- pattern similar to the RLN supply in the tra- ever, in some cases, RLN afferents may be re- chea. Pressure receptors were found in both sponsible. In the case presented, injection of SLN and RLN afferents. Probing the subglottis lidocaine into the RLN arrested the laryngo- was found to be the most effective stimulus spasm. This conclusion is in disagreement for RLN afferents. The same investigators de- with other reports, that defined laryngospasm tected the presence of rapidly adapting mech- as a response to SLN stimulation only.’ Fu- anoreceptors in RLN nerve endings.ll ture basic research will help to verify these Kirchner and Wyke3-6 studied laryngeal ar- preliminary observations in the human larynx titular reflexes in a series of studies published and further elucidate the pathophysiology of in the 1960s. They dissected the cricothyroid laryngospasm. and cricoarytenoid joints of cats and directly stimulated the articular nerves with bipolar electrodes. They showed that afferent im- REFERENCES pulses in the laryngeal articular nerves were able to stimulate contraction of intrinsic la- 1. Olsson GL, Hallen B: Laryngospasm during anesthe- ryngeal muscles. 5 The articular nerves ap- sia. A computer-aided study in 136,929 patients. Acta peared to be similar to afferents present in the Anaesthesiol Stand 28:567-575, 1984 2. Suzuki M, Sasaki CT: Laryngeal spasm: A neuro- joints of the limbs. It was also shown that the physiologic redefinition. Ann Otol Rhino1 Laryngol 86: cricothyroid joint contains afferents destined 150-157,1977 for the RLN. 3. Kirchner JA, Wyke B: Afferent discharges from la- 52 SERCARZ ET AL ryngeal articular mechanoreceptors.