Hypersensitivity Pneumonitis Secondary to… Oyster Mushrooms 4/29/2019

Today we went over a case from the HumanDx Project (Credit goes to Dr. Maki Cronin, SSM Health St. Louis University Hospital). A young woman presents with 5 months of cough, dyspnea, and unintentional weight loss over the past 5 months in setting of working at an in-door oyster mushroom farm for the past 8 months. She was tachycardic and febrile on presentation, with crackles and clubbing on exam. CT revealed e/o fibrosis and GGO, and BAL revealed significant lymphocytosis. This presentation is consistent with a diagnosis of hypersensitivity pneumonitis, and more specifically, mushroom worker’s lung!

Hypersensitivity Pneumonitis (HP)

This condition has many faces/names:

  • Bird fancier’s lung (feathers, bird droppings)
  • Cheese-washer’s lung (Cheese Fancier per Sarasa)
  • Coffee worker’s lung
  • Compost lung (aspergillus)
  • Farmer’s lung (moldy hay)
  • Hot tub lung (hot tubs)
  • Mushroom worker’s lungs (mushroom)
  • Sauna worker’s lungs (contaminated sauna water)
  • Wine-grower’s lung (moldy grapes)


  • 300 known antigens so far, most common (accounting for 75%) are:
    • Farming
    • Birds
    • Water contamination


  • Hypersensitivity to an environmental antigen leading to a type IV hypersensitivity reaction (they love asking these questions on tests for some reason) in genetically susceptible patients
    • Type 1: IgE mediated, immediate onset (min to hours)
      • Ex: Food allergies, PCN allergy, insect sting
    • Type 2: Cytotoxic hypersensitivity, Ab-mediated cell destruction
      • Drug induced cytopenias, Graves thyroiditis
    • Type 3: Immune complex formation
      • Ex: serum sickness, Arthus reactions, vasculitis, drug fever
    • Type 4: Cell-mediated delayed hypersensitivity
      • Activation of T-cells
      • Hours or days after antigen exposure
      • Ex: Tuberculin sensitivity, contact dermatitis, HP
  • Interstitial inflammation and infiltration with lymphocytes, later on granulomas and fibrosis develop over time


  • Acute:
    • Occurs in sensitized pts with high level antigen exposure
    • Fever, chills, cough, chest tightness, dyspnea, nausea 4-8 hours after exposure
    • Exam: Tachypnea, inspiratory crackles, no wheezing
  • Chronic:
    • Occurs in pts with long-term low-level exposure
    • Months to years onset of exertional dyspnea, cough, fatigue, weight loss
    • Clubbing, fevers are uncommon but can happen
    • Over time: Pulmonary fibrosis, resp failure
  • Subacute:
    • Falls between acute and chronic forms


  • A combination of clinical suspicions with exposure history, with assistance of imaging
  • CXR: Neither sensitive nor specific, may show reticular or nodular opacities
  • HRCT: typically shows profuse centrilobular nodules, predominantly GGO, more chronic exposure will lead to fibrosis, traction bronchiectasis
    • Mosaic pattern with areas of GGO is classic
    • More chronic picture leads to fibrosis, which can lead to traction bronchiectasis
    • Bronchiectasis is a chronic condition where the walls of the bronchi are thickened from inflammation and infection.
  • PFT: Can be obstructive, restrictive, or mixed. Obstruction more commonly seen in chronic.
  • BAL: Very sensitive but non-specific.
    • BAL lymphocytosis (often greater than 50%) is helpful but non-specific. Can also see lymphocytosis in COP and NIP but not this high.
  • Biopsy: Rarely done
  • Antigen-specific immunoassays: very high false positive rate, role unclear.


  • Corticosteroids, usually pred 60 1-2 weeks, then tapered over 2-4 weeks for acute/subacute cases
  • Chronic: Longer course of prednisone
  • Remove from environmental exposure ASAP


  • Reversible if detected early and antigen exposure is eliminated
  • Chronic: leads to fibrosis, which is NOT reversible.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s