Final answer:
The steeple sign on an x-ray is characteristic of croup, a respiratory condition typically caused by parainfluenza virus and presenting with symptoms like a barking cough and hoarse voice.
Step-by-step explanation:
The steeple sign seen on a lateral neck x-ray is indicative of a narrowing of the upper airway, which is typically associated with croup (laryngotracheobronchitis), an infection that is often caused by the parainfluenza virus. Croup is common among children and can lead to a barking cough, stridor, and hoarseness. Distinguishing between other respiratory conditions is important for the appropriate treatment. For example, epiglottitis, which is potentially life-threatening, is commonly caused by Haemophilus influenzae type b and presents with a swollen and inflamed epiglottis. Bronchiolitis is generally caused by the Respiratory Syncytial Virus (RSV) and affects the small airways in the lungs, also known as bronchioles. Asthma is a chronic condition that involves the narrowing of airways due to inflammation and can lead to wheezing and difficulty breathing but does not present with a steeple sign. Therefore, the correct answer to the question, 'Lateral neck x-ray shows a steeple sign,' is b) Croup.