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)

Epidemiology

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

Pathophysiology

• 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

Presentation

• 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

Diagnosis

• 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.

Management

• 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

Prognosis

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