16th January 2024

Presentation

Traditionally, the clinical presentation of HP has been classified as acute, subacute, and chronic. Recent classification systems now consider separate phenotypes dependent on the presence or absence of fibrosis, thus categorising HP as fibrotic and non-fibrotic.

HP presents heterogeneously; common symptoms of both fibrotic and non-fibrotic disease include dyspnoea and chronic cough. Less common symptoms include constitutional symptoms such as fever, weight loss and malaise. 

Acute presentations are more in keeping with non-fibrotic HP, whereas progressive symptoms are more consistent with fibrotic disease. Smoking is found to be a protective factor in developing HP.

Non-fibrotic HP features:

• Acute presentations typically occur 6 to 18 hours following high-level exposure to a causative agent
  • Symptoms may include fever, malaise, cough, and dyspnoea
• Patients may also present sub-acutely with similar progressive symptoms. This occurs over a period of weeks to months
• Physical examination may be normal- but inspiratory crackles and squeaks can be heard due to small airways inflammation

Fibrotic HP features:

• Insidious onset of dyspnoea, cough, anorexia, and weight loss
• Occurs secondary to chronic exposure to the sensitised antigen
• On examination, digital clubbing, focal or diffuse inspiratory crackles, and inspiratory squeaks may also be present. Wheezing is rare.