Instantaneous onset of stridor usually implies an inhaled foreign body. This is accompanied by violent bouts of coughing, and a clear history may be obtained from a witness. Stridor indicates partial obstruction, as complete occlusion of the upper airway is silent. Stridor that develops over a period of a few seconds to minutes may be due to laryngeal oedema from an anaphylactic reaction. This may be accompanied by urticaria and facial oedema. Enquiries should immediately determine known allergens and treatment can be initiated without delay. The most common cause of infantile stridor is laryngomalacia. During inspiration, there is extreme infolding of the epiglottis and aryepiglottic folds due to inadequate cartilaginous support. Head flexion aggravates the stridor, whereas patency of the airway is improved by the prone position and head extension. The stridor gradually resolves in most infants within 2–3 months.

Precipitating factors

Iatrogenic causes of stridor may have clear precipitating factors. Tracheal stenosis may complicate a long period of intubation or tracheostomy. Upper airway obstruction occurring immediately after thyroid surgery may be due to laryngeal oedema, haematoma and bilateral recurrent nerve injury. Patients who have been rescued from fires may suffer inhalation injuries due to the high temperature of inhaled gases.

Associated symptoms

Respiratory obstruction may occur with massive enlargement of the tonsils, e.g. in glandular fever, or when complicated by a retropharyngeal abscess. Patients may notice swelling of the neck in the presence of a goitre and may be either euthyroid or complain of symptoms of abnormal thyroid function (p. 176). Symptoms of joint pains, stiffness and deformities occur with rheumatoid arthritis. Associated stridor can result from cricoarytenoid involvement. Weight loss can be an accompanying feature of malignancy. Hoarseness of the voice is an early symptom of laryngeal carcinoma; stridor occurs as a late feature. Chronic cough with haemoptysis in a chronic smoker usually heralds the onset of bronchial carcinoma. The location of the carcinoma may alter the quality of the wheeze. Partial intraluminal upper airway obstruction from bronchial carcinoma produces stridor, whereas partial lower airways obstruction produces the inspiratory monophonic wheeze. Rapid progressive painless dysphagia occurs with oesophageal carcinoma.

Examination

Inspection

With acute partial upper airway obstruction, patients will often appear very distressed. Immediate assessment for generalised urticaria, facial oedema, hypotension and widespread wheezing will allow the diagnosis of anaphylaxis to be made and appropriate treatment initiated. Soot on the face and singed nasal hair from thermal exposure may be present with inhalational injuries. A large goitre will be visible on inspection. Bilateral symmetrical deforming arthropathy involving the small joints of the hands (MCP, PIP) is suggestive of rheumatoid disease. Clubbing may be present in the fingers with bronchial carcinoma.

The cause of stridor may be visible on inspection of the throat. Further information is obtained on inspection using indirect laryngoscopy. With bilateral vocal cord palsy, the cords lie in a cadaveric position. A small glottic aperture is seen and does not widen on attempted inspiration. Supraglottic and glottic carcinomas may be readily visible.

Palpation and auscultation

The presence of cervical lymphadenopathy may be due to infection or carcinoma of the larynx, pharynx, bronchus or oesophagus. A goitre may also be palpable in the neck, skewing the trachea to one side due to compression effects. The chest is examined for monophonic wheezing, collapse of a segment, pleural effusion and rib tenderness, which are the thoracic manifestations of bronchial carcinoma.