Pediatric Hypersensitivity Pneumonitis Clinical Presentation

Updated: Jan 28, 2022
  • Author: Naga Jaya Smitha Yenduri, MD; Chief Editor: Girish D Sharma, MD, FCCP, FAAP  more...
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A comprehensive environmental history and high index of suspicion are critical for diagnosis. Hypersensitivity pneumonitis (HP) should be considered in patients with chronic or recurrent cough, shortness of breath, or a history of recurrent acute respiratory symptoms without definite infectious triggers.

Inquire about specific exposures; the patient may not volunteer them. Because bird fancier’s lung is the most common hypersensitivity pneumonitis in children, be sure to ask about bird exposure. Contact may not necessarily be in the home and may not be obvious. Exposures may be in or near the home, at school, at play locations, as a part of hobbies, at the place of employment, or anywhere else the child spends time. Repeated questioning, home inspection, and/or inspection of sites where the child spends time may be needed to identify the causative antigen.

As new exposures leading to hypersensitivity pneumonitis continue to be identified, exposure to any area likely to contain high concentrations of respirable organic antigens, particularly fungal or avian antigens, should lead one to include hypersensitivity pneumonitis in the differential diagnosis.

Clues that suggest the diagnosis of hypersensitivity pneumonitis are as follows:

  • History of recurrent pneumonia, particularly with regularity or a pattern

  • Other people at home or school who have similar symptoms

  • Development of respiratory symptoms after the patient moves to a new home or new school

  • Improvement of symptoms when the patient is away from home or school for an extended period

  • Contact with birds

  • Water damage to the patient's home or school facility

  • Use of a hot tub, sauna, or swimming pool

The key to diagnosing hypersensitivity pneumonitis lies in a detailed history. The clinician has to maintain a high index of suspicion. Reaching the diagnosis can be difficult because symptoms are often nonspecific and the available diagnostic tests are imperfect. Taking appropriate, effective action to eliminate the inciting exposure can prevent substantial pulmonary morbidity and mortality.

A multicenter study was designed to derive and validate a clinical prediction rule in adult patients who presented with a pulmonary condition for which hypersensitivity pneumonitis was in the differential diagnosis. The study noted 6 significant predictors of a final diagnosis of hypersensitivity pneumonitis, as follows [69] :

  • Exposure to a known offending antigen

  • Positive precipitating antibodies to the offending antigen

  • Recurrent episodes of symptoms

  • Inspiratory crackles upon physical examination

  • Symptoms occurring 4-8 hours after exposure

  • Weight loss

Although the associated probabilities of hypersensitivity pneumonitis from these predictors cannot be generalized to children who have a different spectrum of illnesses, they are useful questions to incorporate into the history.

Manifestations of hypersensitivity pneumonitis are classified as acute, subacute, or chronic. These classifications should be considered as points along a spectrum of illness rather than clearly delineated, discrete types of illness. [70] This classification is based on clinical presentation, not histopathology. In patients with acute disease, a temporal relation between the respiratory symptoms and antigenic exposure can usually be identified. In cases of subacute or chronic exposure, the association between antigenic exposure and development of disease may not be obvious.


Physical Examination

Acute hypersensitivity pneumonitis is characterized by the abrupt onset (4-6 h after exposure) of fever, chills, malaise, nausea, dry cough, chest tightness, and dyspnea. Physical examination may reveal tachypnea and fine crackles localized to the lung bases; wheezing is unusual. The presentation is easily confused with that of an infectious pneumonia. Removal from exposure usually results in resolution of symptoms within hours to days.

Subacute hypersensitivity pneumonitis is characterized by the gradual development of productive cough, dyspnea, fatigue, anorexia, weight loss, and low-grade fever. Physical examination and chest auscultation may reveal tachypnea and diffuse crackles. In patients with very severe disease, cyanosis may be present. [1]  Resolution of disease may take weeks to months after removal from exposure.

Chronic hypersensitivity pneumonitis may be difficult to diagnose in its early stages. A chronic cough with normal physical examination findings may be the first presentation. Over time, the disease may progress to dyspnea, fatigue, weight loss, and exercise intolerance. Auscultation of the chest may reveal crackles. An “inspiratory squawk” or “chirping rales” have been described. [71, 72]  Digital clubbing may be seen in the advanced stages of the disease.