Although the presenting signs and symptoms of chronic, severe CHP are similar to those of IPF, radiographic findings differ. HRCT studies of patients with CHP demonstrate upper lobe fibrotic changes, whereas patients with IPF demonstrate lower lobe fibrotic changes. In addition, expiratory air trapping is also observed in HRCT studies of patients with CHP, but is not typically present in patients with IPF. Likewise, emphysema is often revealed on HRCT scans of patients with IPF, but rarely in patients with CHP.
Another important characteristic that distinguishes CHP from IPF is its association with a potential provocative agent. CHP results from inhalation of environmental antigens in genetically at-risk individuals. A fulminant autoimmune response to inhaled substances (fungal, bacterial, or chemical) causes inflammation. In the acute and subacute stages of CHP, symptom onset is gradual and includes cough, exertional dyspnea, and weight loss. Long-term inflammation leads to fibrosis, and it is at this later stage of CHP that symptoms mimic IPF. A detailed personal, social, and occupational exposure history is key to determining initial antigens, including aviculture, work-associated chemical exposures, exposure to hay, and other, more obscure triggers.
Saddle PE is not present in patients with CHP, and unilateral lower lobe infiltrate is not present in patients with IPF.
For more on the differential diagnosis of CHP, read here.
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Cite this: Guy W. Soo Hoo. Fast Five Quiz: Idiopathic Pulmonary Fibrosis Differential Diagnosis - Medscape - Nov 20, 2019.
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