Interstitial lung disease Flashcards
What are interstitial lung diseases?
AKA dissuse parenchymal lung diseases
Heterogenous group of conditions that cause varying degrees of inflammation and fibrosis which initially affects the interstitium of the lung (tissue space around alveoli)
What is sarcoidosis?
Immunological disorder that results in the formation of small nodules throughout the body
Most common in African American women
Immune response occurs in the absence of a pathogen
How is interstitial lung disease classified?
A) IPF of known causes/ associations: connective tissue/ autoimmune, exposures (e.g. asbestos), drugs (methotrexate)
B) Idiopathic interstitial pneumonias
C) Granulomatous disease: sarcoidosis, hypersensitivity pneumonitis, infections, vasculitis
D) Rarer causes
Pathology of sarcoidosis
T-cells and macrophages become attracted to a particular part of healthy tissue (most commonly hilar LNs)
Immune cells gather in certain spots and form granulomas that have T-cells around periphery and macrophages in the centre
Overtime the granulomas cause LNs to enlarge and cause bilateral hilar lymphadenopathy
Where does sarcoidosis usually affect?
Lungs: causing hilar lymphadenopathy
Skin nodules: erythema nodosum, caused by inflammation of fat within skin
Eyes: uveitis (inflammation of pigmented areas of eyes)
Heart: causing arrhythmias
What are the symptoms of sarcoidosis?
General: fever, weightloss, fatigue
Specific: SOB, cough, tender leg nodules, vision changes
What is idiopathic interstitial pneumonia?
Interstitial lung diseases of unknown cause
Which is the most common idiopathic interstitial pneumonia?
Idiopathic pulmonary fibrosis
A progressive and ultimately fatal disease of unknown cause
M:F 2:1
What is the histological finding in idiopathic pulmonary fibrosis?
Usual interstitial pneumonia
Key features: heterogenous appearance with areas of normal lung and areas of marked fibrosis
What is the pathophysiology of idiopathic pulmonary fibrosis?
Believed that unidentified environmental cause repeated injury to alveolar epithelium
Wound healing mechanisms get out of hand and over-production of fibroblasts and deposition of ECM in the interstitium occurs.
Loss of elasticity and impaired gas exhange leads to progressive respiratory failure
What are the clinical features of idiopathic pulmonary fibrosis?
- Progressive dyspnoea that may be accompanied by a cough
- Patients often treated for heart failure and chest infections before diagnosis of IPF
- Onset during 60s
- Finger clubbing in 25-50%
- Pulmonary hypertension
Investigations for idiopathic pulmonary fibrosis
Aim is to confirm the presence of fibrosis and exclude identifiable/ reversible causes
Respiratory function tests: show reversible pattern
Bloods: to exclude autoimmune disease
Chest x-ray: small volume lungs with increased shadowing at bases
HRCT: imaging of choice
What is the median survival time of IPF?
2-5yrs
Treatment of IPF
PIRFENIDONE: antifibrotic agent which slows the rate of FVC decline
NINTEDANIB: intracellular inhibitor of tyrosine kinase which is thought to activate cellular signalling responsible for uncontrolled fibroproliferation
Treatment for GORD because this is thought to add to alveolar damage
What is hypersensitivity pneumonitis?
One of the granulomatous interstitial lung diseases
Caused by an allergic reaction to an inhaled antigen or ingestion of a causative drug
Common antigens that cause hypersensitivity pneumonitis diseases
Farmer’s lung: mouldy hay or veg
Bird fancier’s lung
Humidifier fever: bacteria or amoeba in air conditioners
Cheese washer’s lung: mouldy cheese
Winemaker’s lung: mould on grapes
Discuss the pathogenesis of hypersensitivity pneumonitis
Histological features: chronic inflammatory infiltrate, poorly defined interstitial granulomas, interstitial fibrosis and honeycomb change
Immune reaction involves cellular immunity and deposition of immune complexes which causes inflammation through the activation of complement via the classical pathway
Clinical features of hypersensitivity pneumonitis
Categorised based of symptom severity
Acute: symptoms 4-6hrs following exposure, fever, resolution 24-48hrs after antigen is removed
Subacute: occurs with intermittent or lower level exposure, improvement seen weeks-months following removal from exposure
Chronic: usually no preceeding hx of acute symptoms, finger clubbing may be present
Investigations for hypersensitivity pneumonitis
- Take a detailed exposure hx
- Chest x-ray: not great at identifying HP
- HRCT: nodules with ground-glass opacity and evidence of air trapping
- Lung function tests: not diagnostic but identify degree of impairment
- Precipitating antibodies against specific antigens
How is hypersensitivity pneumonitis managed?
- Remove exposure to inciting antigen
- Prednisolone if removal of exposure doesn’t improve symptoms
What is a granuloma?
Mass or nodule composed of chronically inflamed tissue formed by the repsonse of macrophages to an antigen
Characterised by the presence of epithelioid multinucleate giant cells
Why do granulomas form?
Granulomas form to confine a pathogen and limit the extent of surrounding inflammation and tissue destruction
