Interstitial lung disease

Question 1

What are interstitial lung diseases?

Answer 1

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)

Question 2

What is sarcoidosis?

Answer 2

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

Question 3

How is interstitial lung disease classified?

Answer 3

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

Question 4

Pathology of sarcoidosis

Answer 4

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

Question 5

Where does sarcoidosis usually affect?

Answer 5

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

Question 6

What are the symptoms of sarcoidosis?

Answer 6

General: fever, weightloss, fatigue

Specific: SOB, cough, tender leg nodules, vision changes

Question 7

What is idiopathic interstitial pneumonia?

Answer 7

Interstitial lung diseases of unknown cause

Question 8

Which is the most common idiopathic interstitial pneumonia?

Answer 8

Idiopathic pulmonary fibrosis

A progressive and ultimately fatal disease of unknown cause

M:F 2:1

Question 9

What is the histological finding in idiopathic pulmonary fibrosis?

Answer 9

Usual interstitial pneumonia

Key features: heterogenous appearance with areas of normal lung and areas of marked fibrosis

Question 10

What is the pathophysiology of idiopathic pulmonary fibrosis?

Answer 10

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

Question 11

What are the clinical features of idiopathic pulmonary fibrosis?

Answer 11

• 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

Question 12

Investigations for idiopathic pulmonary fibrosis

Answer 12

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

Question 13

What is the median survival time of IPF?

Answer 13

2-5yrs

Question 14

Treatment of IPF

Answer 14

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

Question 15

What is hypersensitivity pneumonitis?

Answer 15

One of the granulomatous interstitial lung diseases

Caused by an allergic reaction to an inhaled antigen or ingestion of a causative drug

Question 16

Common antigens that cause hypersensitivity pneumonitis diseases

Answer 16

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

Question 17

Discuss the pathogenesis of hypersensitivity pneumonitis

Answer 17

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

Question 18

Clinical features of hypersensitivity pneumonitis

Answer 18

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

Question 19

Investigations for hypersensitivity pneumonitis

Answer 19

• 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

Question 20

How is hypersensitivity pneumonitis managed?

Answer 20

• Remove exposure to inciting antigen
• Prednisolone if removal of exposure doesn’t improve symptoms

Question 21

What is a granuloma?

Answer 21

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

Question 22

Why do granulomas form?

Answer 22

Granulomas form to confine a pathogen and limit the extent of surrounding inflammation and tissue destruction