Background

Vocal cord paralysis (VCP) is the manifestation of the disease rather than a disease in itself, characterized by the loss of the movement of one or both of the vocal cords. The restriction in the movement of vocal cords can be unilateral (UVCP) or bilateral (BVCP). The presenting features and the management protocol of the patients are different for UVCP and BVCP. The UVCP patients may be asymptomatic or can present with the varying degree of dysphonia (breathy voice, vocal fatigue to complete aphonia), dysphagia and aspiration [1,2,3]. Similarly, the patients with BVCP may present with stridor, snoring, difficulty in swallowing and aspiration in addition to the dysphonia as present in UVCP [4,5,6]. The presence of stridor and need for immediate intervention has made BVCP as one of the emergencies in the Laryngology practice. The presence of recurrent cough, fever and pneumonia can also sometimes be the presenting features of the VCP [3, 7,8,9].

The etiology of the VCP has a very important role to play in the management process for both UVCP or BVCP [4, 5, 10, 11]. Hence, detail evaluation has to be done for any case of VCP to find out the definitive etiology responsible. The management of the etiological factors, causing VCP, alone may sometimes be the complete treatment for VCP. The imaging modalities like computed tomography (CT) scan, magnetic resonance imaging (MRI) and modified barium swallow (MBS), in addition to consultation with various other specialties such as neurology, gastroenterology, pulmonology, cardio vascular surgery, or spine surgery are required most of the times to ascertain the main cause responsible for VCP [1, 5, 11,12,13].

The VCP results primarily due to the neurological or the mechanical cause. Any type of trauma (iatrogenic or non-iatrogenic) or pathology in the motor cortex, skull base, neck, and mediastinum that leads to the disruption of the function of recurrent laryngeal nerve (RLN), constitute the neurological etiology. Similarly, the mechanical etiology incorporates the loss of movement of the vocal cords as a result of infiltration of the muscle of the vocal cords or ankyloses of the cricoarytenoid joint. The type of the vocal cord paralysis, whether it is due mechanical fixation of the vocal cords (for example, cricoarytenoid joint fixation or muscle infiltration) or due to the neurological cause, is evaluated with the detailed study of the characteristics of vocal cord vibration during the videolaryngostroboscopy (VLS). There have been multiple studies suggesting various etiological factors responsible for VCP, often without proper agreement on the most common etiology [1, 3, 4, 10, 14,15,16,17]. There also are studies that have evaluated the changing trend in the etiology of VCP over the time period [1, 12, 13, 16, 18]. The present study evaluates the etiology and presenting features of the UVCP and BVCP patients over the 22 years at a single institute. The study also explores the change in the trend over the 22 years in the etiology and presenting features of the VCP patients.

Methods

This was a retrospective study conducted at the Laryngology department of the Deenanath Mangeshkar Hospital and Research Center, Pune, India (referred as ‘hospital’ from here on). It is a review article which studied the etiology and presenting features of vocal cord paralysis from March 1998 to March 2020. Approval for the study was granted by the Institutional Ethics Committee of the hospital. The primary objective of the study was to analyze the etiology and presenting features of VCP and to look into the changing trend of etiology and presenting features over the above-mentioned time frame.

Adhering to the objectives, details of the VCP patients were retrieved from the hospital database. Patients of all ages and genders with VCP who underwent evaluation at the hospital from March 1998 to March 2020 were included in the study. The detailed history taking and examination was done for all the patients of VCP. The VLS was routinely performed for every VCP patient. The imaging modality like CT scan, MRI, and MBS along with the necessary blood investigations were performed in the VCP patients in order to find out the etiology. Consultations were done with other departments such as neurology, pulmonology, cardiovascular surgery, spine surgery, and gastro enterology for evaluating the VCP patients. The combined team approach was utilized to evaluate the etiology for VCP.

The records of 711 patients were included in the study. The patients were divided into 2 groups for studying the change in the trends in etiology and presenting complaints of VCP. The first group consisted of 272 (38.3%) patients from March 1998 to March 2009 and second group consisted 439 (61.7%) patients from April 2009 to March 2020. The history and examination sheet, the investigation profile and all the imaging of patients were reviewed. The reference note from other concerned departments were also reviewed. The demographic details, gender, presenting complain, age at the presentation, diagnosis, type of paralysis (unilateral or bilateral), and side of paralysis for unilateral paralysis were documented. For every VCP patients, the VLS was studied and the vocal cords vibratory patterns were evaluated in the presence of consultant laryngology surgeon in order to differentiate between the mechanical and neural cause of VCP. The etiology of the VCP was documented under two broad headings such as surgical and non-surgical etiology separately for UVCP and BVCP respectively. The etiology was defined as idiopathic, if after the complete evaluation and consultation with other departments, there was no established cause identified. The collected information was analyzed between the first and second groups to evaluate the changing trend in the etiology and presenting complaint of the VCP patients.

Results

The mean age of the patients included in the study was 47 ± 9.2 (range 2 months to 91 years, median 45 years). There were 451/711 (63.4%) males and 260/711 (36.6%) females. The first group consisted of 229 (84.2%) with UVCP and 43 (15.8%) with BVCP. Similarly, the second group consisted of 342 (77.9%) patients with UVCP and 97 (22.1%) patients with BVCP. Out of the total 571 patients with UVCP, the left sided paralysis was present in 343 (60.1%). The presenting features and their duration of onset in the patients with UVCP and BVCP are as shown in Figs. 1 and 2 respectively. The surgical and non-surgical etiologies of UVCP and BVCP are as shown in Tables 1 and 2 respectively.

Fig. 1
figure 1

Presenting features and duration of onset (with their SD) in UVCP

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Fig. 2
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Presenting features and duration of onset (with their SD) in BVCP

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Table 1 Surgical and non-surgical etiology of UVCP
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Table 2 Surgical and non-surgical etiology of BVCP
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The dysphonia was most common presenting feature in UVCP and BVCP with 67.2% in first and 70.5% in second group for UVCP and 95.3% in first and 91.7% in second group for BVCP. The frequency of all the presenting features in both the groups were comparable for both UVCP and BVCP. However, the duration of symptoms onset at the time of presentation, for all the symptoms, was less for second group in comparison to first group for both the UVCP and BVCP respectively.

In surgical etiology, the thoracic surgery included surgeries such as pulmonectomy (1.7% in the first and 2% in the second group), thoracotomy and pericardiocentesis (0.4% and 1.7%), mediastinal mass excision (1.3% and 1.7%), esophagectomy and gastric pull up (1.7% and 2.3%), aortic aneurysm repair (1.3% and 1.2%), and implantation of vagal nerve simulator (0.4% and 0). CNS pathology included conditions such as motor neuron disease (0 and 0.3%), myasthenia gravis (0.8% and 1.4%), post-viral neuritis (1.7% and 1.7%), cerebro vascular accident (CVA) (0.4% and 0.3%), and pontomedullary glioma (0 and 0.3%). The miscellaneous in non-surgical etiology included conditions such as coarctation of aorta (0.4% and 0.6%), pulmonary hypertension leading to right ventricular hypertrophy (0.4% and 0.3%), aberrant azygous vein (0 and 0.3%), and aortic aneurysm (0 and 0.3%).

Discussion

The VCP is not an infrequent condition encountered during the laryngology practice with study suggesting 0.42% of total new patients [11]. The age and gender of the VCP patients as shown in the current study are comparable as shown by other researches [10,11,12,13,14, 19, 20]. Our study showed 19.7% of the VCP patients were having BVCP, similarly Laura H. Swibel Rosenthal et al. [13], Albert L Merati et al. [12], and Hsin Chien Chen et al. [20] reported BVCP in 17%, 11%, and 11% of VCP patients respectively. The left VCP was more common than right VCP as shown by the current, and other studies [11, 15, 16, 21]. The reason for this could be the longer course of left RLN which leads to more probability of it getting injured during any pathology in the lower neck and mediastinum. The course of right RLN such as, making angle of around 45 degree while entering the tracheo-esophageal groove and the variation in the branching pattern in relation to the inferior thyroid artery often renders it more vulnerable to injury during the neck surgeries [22,23,24].

The dysphonia was the most common presenting complain in both the UVCP and BVCP. David M. Simpson et al. [25], Brian C Spector et al. [26], and Jaya Gupta et al. [10] in their study have reported dysphonia to be the most common presenting feature of UVCP. In contrast to the current study, John M. Feehery et al. [18] and Jaya Gupta et al. [10] have reported difficulty in breathing to be the most common presenting complaint in BVCP. For both the first and second group the frequency of the presenting complaints was comparable in our study. However, the duration of onset of the symptoms was less for the second group as compared to the first group. The reason for this was felt to be increased awareness among the patients about the condition and also the increased accessibility of the hospitals to the patients. Vague symptoms such as dysphagia, aspiration and cough had maximum duration of onset for both UVCP and BVCP. The alarming symptoms such as stridor and aspiration as expected were the ones with shortest duration of onset.

The patients of VCP were routinely investigated using various imaging modalities such as CT scan, MRI and MBS in order to find out the etiology behind the VCP. The imaging modalities helped to search for any pathology, responsible for causing VCP. The electromyography as used by Vyas M. N. Prasad et al. [19] in their study was not used in current study. There was increase in the surgical etiology for UVCP and BVCP in second group when compared to the first group. Our study demonstrated increase in the total number of thyroid and parathyroid surgery (31 vs 64) resulting in UVCP in second group compared to the first group. The number of the thyroid surgery causing UVCP was almost increased by twice (27 vs 53), however the percentage of thyroid surgeries causing UVCP only increased by 3.7%. Similarly, the number of thyroid and parathyroid surgeries causing BVCP was also increased by more than double in second group (16 vs 38), though the percentage increment was mere 1.9%. The reason for the relatively less increment in percentage could be increase in total number of VCP (272 vs 439) alongside the individual etiology in the second group. There was also increase in number of patients with parathyroid surgery as etiological factor for VCP in second group. Laura H. Swibel Rosenthal et al. [13], in their study, have shown the doubling in the number of surgical etiologies for UVCP during the year 1996 to 2005 when compared to 1985 to 1995. This was thought to be due to the increase in the number of the surgeries performed during this time period.

The total number of non-surgical etiology were decreased, as shown by our study, in second group when compared to the first group for both UVCP and BVCP. There was decrease in the idiopathic cases in the second group UVCP (from 27.9% in first group to 19.9% in the second group) and BVCP (from 11.7 to 10.3%). The improved diagnostic modalities in the recent times were the reason for this decrease in the number. There was an increase in the number of UVCP due to trauma, which can be attributed to increased road traffic accident in the recent times [27]. The decrease in the number of laryngeal malignancy cases causing UVCP and BVCP was thought to be due to the early diagnosis and treatment of laryngeal malignancy. There was also an increment in the number of patients with UVCP and BVCP in second group following radiotherapy. This was due to the shifting paradigm of malignancy management towards, conservative and organ preservation approach in the recent times. The better community level management of pulmonary tuberculosis (TB) was the reason behind the decreased pulmonary TB etiology in the second group. As most of the TB cases in the recent times are treated at very early stage unlike the scenario in the past. The similar findings were also demonstrated by Laura H. Swibel Rosenthal et al. [13] in their study, however there was decrease in number of trauma cases as the etiological factor of UVCP during the time period 1996 to 2005. The trend of changes in the etiology of UVCP and BVCP over the time period by various study is as shown in Table 3.

Table 3 Etiology of UVCP and BVCP by various studies over the different time period
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There was increase in the number of thyroid surgeries as the etiological factor for UCVP and BVCP over the time period as shown in the Table 3. The non-thyroid surgeries have been seen to have constant variation throughout the mentioned time frame. The idiopathic cause shows the decreasing trend in UVCP as shown by various studies. In case of BVCP, the idiopathic causes have shown constant variation over the time period.

The present study was the largest study found in the literature that has shown the changing trend of etiology and presenting features of UVCP and BVCP, over the time duration of 22 years. This study also had the largest sample size of the VCP patients in comparison to other similar studies found in the literature. The retrospective nature of the data collection and lack of the follow up data was felt to be the limiting factor of the present study. Hence, the recommendation has been put forward in the future, for a prospective research with proper long-term follow-up for better understanding of the subject matter.

Conclusions

The most frequent etiological factor for UVCP was non-surgical, with idiopathic being the commonest, in the surgical etiology thyroid and parathyroid surgery were the commonest. The BVCP was most often caused by surgical etiology, with thyroid and parathyroid surgery being the commonest and malignancy being the commonest non-surgical etiology. For both the UVCP and BVCP, there was increasing trend for surgical and decreasing trend for non-surgical etiology over the time period. The VCP was found to be detected earlier than before with dysphonia being the commonest presenting complain. The prospective research with increased sample size has been suggested in the future for better understanding the changing trend of etiology and presenting complain.