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Læknablaðið 2007; 93: 17-20

A fifty six year old woman with history of asthma visited a respiratory specialist. She had been diagnosed with asthma more than a year previously in a primary care clinic. She was treated with inhaled medications without good response. A respiratory specialist diagnosed tracheal narrowing secondary to thyroid enlargement that was pushing the trachea together. She was cured with a thyroid operation. Discussed are differential diagnosis of asthma and causes of airway narrowing and the importance of spirometry in diagnosing asthma.

Keywords: case report, asthma, airway narrowing, spirometry.

Correspondence: Gunnar Guðmundsson

 

Figure 1. A Flow-volume loop from the patient. It shows flattening of both the inspiratory and expiratory limbs.

 

Figure 2. Computerised tomography of cervical structures and upper thorax. The diameter of the right lobe of the thyroid gland measures upp to 110 mm in cephalo-caudal direction and the diameter of the traceal lumen is just 5,6 mm.

 

Figure 3. Histology. Microscopic examination showed multiple variably sized nodules composed of variably sized thyroid follicles consistent with multinodular goiter.

 

Figure 4. A normal flow-volume loop. The respiratory flow is plotted on the Y-axis against the respiratory volume on the X-axis. Flow in inspiration is negative on the Y-axis wheras expiratory flow is positive. With maximal inhalation the value on the Y-axis is 0 and it increases during expiration. The flow rises rapidly early in expiration to a maximal value:  Peak expiratory flow (PEF). It then falls linearly during exhalation toward 0 when Forced Vital Capacity (FVC) has been reached and only Residual Lung Volume is left.

 

Figure 5. Flow-volume loops in upper airway obstruction. With a narrowing of the airway, its resistance increases which causes a decrease in flow, because flow has an inverse relationship to resistance. Importantly, the flow diminishes variably depending on the type of the obstruction, both its location and fixability. A: In a fixed airway obstruction both the expiratory and the inspiratory limbs are flat due to diminished flow. B: In a dynamic extrathoracic airway obstruction the expiratory limb of the flow-volume curve is normal but only the inspiratory limb shows a flattening. C: In a dynamic intrathoracic airway obstruction the inspiratory limb is normal but the expiratory limb shows a flattening.

 

Table I.

 

	Normal lung function	Obstructive	Restrictive
FVC	> 80% of predicted value	Diminished	More diminished
FEV1	> 80% of predicted value	More diminished	Diminished
FEV1/FVC ratio	> 80%	<70%	>80%