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Journal of Postgraduate Medicine, Vol. 54, No. 2, April-June, 2008, pp. 82-83 Guest Editorial Upper airway obstruction due to goiter: An overlooked problem! Bonnema SJ Department of Endocrinology and Metabolism, Odense University Hospital Code Number: jp08034 The anatomical relationship between the thyroid gland and the trachea is of great clinical importance. The intra-tracheal air flow rate may be critically compromised if the lumen is deformed by a goiter. The prevalence of upper airways obstruction due to thyroid enlargement is very poorly known and most of the previous studies are done in a small number of selected patients. In a study from the UK one-third of consecutive patients with goiter had upper airway obstruction detected by lung function tests. [1] Surprisingly, these patients did not have more respiratory complaints than did patients with a normal lung function. This is probably explained by the fact that the thyroid enlargement usually develops over years and the patient may get used to the condition. Thus, many individuals presenting with goiter do not have respiratory symptoms and the airway obstruction must be detected by use of other methods. Imaging of the trachea can be done by plain X-ray, computerized tomography (CT), magnetic resonance imaging (MRI) and to some extent ultrasound. Plain X-ray has a low sensitivity and shows poor correlation with the air flow rate. [2] The cross-sectional area of the trachea can be measured by CT or MRI. Studies using these methods have been conflicting as regards the correlation to the air flow rate, [2],[3] probably due to a relatively low precision of theimaging. [4] Confounding factors may be changes of the tracheal lumen caused by the respiration itself, the applied intrathoracic pressure and the position of the patient. Furthermore, even with a small increase of the tracheal area the flow rate becomes much less dependent of the luminal space according to Poiseuilles Law (flow proportional to radius 4).Thus, it seems evident that tracheal imaging cannot stand alone and a lung function test should be considered in patients with a large goiter. However, this is rarely done in the routine diagnostic setup. In this issue of the Journal of Postgraduate Medicine Pradeep and co-workers [5] present a prospective study of 64 patients with goiter and the effect on the lung function following thyroidectomy. The study is until now the largest of its kind. Noteworthy, the patients did not have respiratory complaints at inclusion. After thyroidectomy, improvements were found in the tidal volume and in some expiratory parameters among females and in the airway resistance among men, respectively. [5] Unfortunately, the inspiratory function was not monitored and if done it might have revealed an even greater benefit from the operation. The study included an assessment of the tracheal diameter by X-ray but this variable was not part of the follow-up. A favorable effect on the respiration following treatment of the goiter was reported more than 30 years ago [6] and has been verified in subsequent studies. In one study [7] a 25% increase of the maximal inspiratory flow rate was found after thyroidectomy, even in patients with a normal tracheal radiogram preoperatively. No study of thyroidectomized patients has been performed in which both the lung function and the tracheal area were monitored. 131 I therapy is also effective in this context. In two previous studies [3],[8] in patients with large goiters radioiodine therapy resulted in an increase of the cross-sectional area of the trachea (determined by MRI) by 17-36% which correlated with the goiter reduction. The inspiratory capacity improved by 20-25% without any change of the expiratory parameters. [3] It is likely that the exact topo-anatomical relationship between the goiter and the trachea plays a role. Thus, the benefit resulting from goiter shrinkage/removal should theoretically be greater if the trachea is encircled by the thyroid rather than just displaced from the midline, but no studies have evaluated this aspect. Most studies have shown that goiter reduction improves mainly the inspiration and to a lesser extent the expiration. During inspiration the higher air flow through a stenotic passage induces a negative transmural pressure gradient across the tracheal wall and this may cause a partial collapse of the tracheal cartilage. During expiration the drop in the transmural pressure is less critical since the pre-stenotic (i.e. intrathoracic) air pressure is abovetheatmospheric level. Thus, a lung function test should include the inspiratory phase of the respiration and a flow volume loop is recommended for this purpose. The study by Pradeep et al. , [5] emphasizes that upper airway obstruction is present in a significant fraction of patients with goiter, but this problem is probably overlooked by many clinicians. Since it seems well proved by this [5] and other studies [3],[6],[7],[8] that goiter treatment improves the respiratory function, this is a strong argument for following an active therapeutic strategy- even in relatively asymptomatic patients. References
Copyright 2008 - Journal of Postgraduate Medicine |
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