Differentials
Idiopathic non-specific interstitial pneumonia
SIGNS / SYMPTOMS
More commonly associated with collagen vascular disease; therefore, patients may have skin, joint, or other systemic manifestations. Clinical progression is highly heterogeneous; a subset of patients progress to end-stage fibrosis.[43]
INVESTIGATIONS
More ground-glass opacities on chest CT, absence of honeycombing.
Presence of auto-antibodies if secondary to an underlying connective tissue disease.[43]
Cryptogenic organising pneumonia (formerly known as bronchiolitis obliterans organising pneumonia [BOOP])
SIGNS / SYMPTOMS
More commonly associated with prior infection or collagen vascular disease.
Considered an acute/subacute idiopathic interstitial pneumonia.[43]
Systemic manifestation of weight loss, fever, joint symptoms, and rash are more common.[59]
INVESTIGATIONS
Patchy consolidation, isolated nodules, or infiltrative reticulation on chest CT.[59]
Acute interstitial pneumonia (AIP)
Respiratory bronchiolitis interstitial lung disease
Desquamative interstitial pneumonia
Lymphoid interstitial pneumonia
Connective tissue disease-associated interstitial lung disease
SIGNS / SYMPTOMS
Skin, joint, or other serological abnormalities will be present.[61]
Rash may be present.
INVESTIGATIONS
May have less 'typical' chest CT with less peripheral predominance.
Presence of autoantibodies related to connective tissue.
Drug-related pulmonary fibrosis
SIGNS / SYMPTOMS
Respiratory symptoms similar to those of IPF will be related to exposure to medications such as amiodarone, nitrofurantoin, and bleomycin, which are thought to cause pulmonary fibrosis.
INVESTIGATIONS
Chest CT and pulmonary function tests are non-specific.
Asbestosis
SIGNS / SYMPTOMS
History of asbestos exposure.
Physical findings will be normal in pleural disease unless the pleural thickening is diffuse or there is a benign pleural effusion. In these cases, breath sounds will be diminished on auscultation and dullness to percussion may be present.
INVESTIGATIONS
Pleural plaques may be present on chest imaging; ferruginous bodies can be found on biopsy.[61]
Hypersensitivity pneumonitis
SIGNS / SYMPTOMS
Respiratory symptoms are typically associated with acute exposure to causal antigen such as bacteria or mould in silage or hay.
INVESTIGATIONS
Presence of IgG antibodies in the blood to the causal antigen, a ground-glass appearance on high-resolution CT, and granulomas on lung biopsy.
Sarcoidosis
SIGNS / SYMPTOMS
Extra-pulmonary involvement.
By comparison with IPF, younger patients affected.
INVESTIGATIONS
Lymphadenopathy is more evident on chest imaging.[61]
Langerhans' cell histiocytosis
SIGNS / SYMPTOMS
Rare disease.
History of smoking and spontaneous pneumothorax.
INVESTIGATIONS
Cystic disease with nodules in upper- and mid-lung zones on chest CT.
Lymphangioleiomyomatosis
SIGNS / SYMPTOMS
Rare disease.
Pre-menopausal women are affected; spontaneous pneumothorax is common.
INVESTIGATIONS
Thin-walled cystic disease throughout the lung; combined obstruction and restriction on pulmonary function tests.
Combined pulmonary fibrosis and emphysema
SIGNS / SYMPTOMS
Patients are predominantly male and have a history of smoking.
Severe dyspnoea, exertional hypoxaemia, and pulmonary hypertension are common. Spirometry changes are often more variable.[62]
Prognosis is dismal.
INVESTIGATIONS
Characterised by relatively preserved airflow rates and lung volumes on spirometry; severely impaired DLCO.[62]
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