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Viral & Autoimmune Causes

TL;DR

Myocarditis: Viral & Autoimmune Causes is a frequently tested MRCP Part 1 topic that requires recognition of clinical patterns rather than memorisation. Viral causes (especially Coxsackie B) dominate, presenting with chest pain and raised troponin after a prodrome, while autoimmune forms occur in systemic diseases or drug reactions. Cardiac MRI is the investigation of choice, and management is largely supportive. Differentiating myocarditis from acute coronary syndrome is a key exam skill.


Why this matters

For MRCP Part 1, myocarditis is a classic “mimic” condition—it can resemble myocardial infarction, heart failure, or arrhythmias. Questions typically test your ability to identify patterns (e.g., viral prodrome + chest pain + normal coronaries) and distinguish between infectious and autoimmune causes.

Use this guide alongside the MRCP Part 1 overview and reinforce concepts with practice from the Free MRCP MCQs.


Core sections

1. Definition and pathophysiology

Myocarditis is defined as inflammation of the myocardium, most commonly due to viral infection but also immune-mediated processes.

Three-phase model (high-yield):

  1. Direct viral injury – cardiomyocyte damage

  2. Immune response – T-cell mediated inflammation

  3. Chronic phase – fibrosis → dilated cardiomyopathy

This progression explains why some patients recover while others develop chronic heart disease.

2. Viral causes (most tested)

Viral infections account for the majority of cases.

Key viruses:

  • Coxsackie B virus (most important for exams)

  • Adenovirus

  • Parvovirus B19

  • Human herpesvirus 6

  • Influenza and SARS-CoV-2

Typical presentation pattern:

  • Recent flu-like illness

  • Chest pain (often pleuritic)

  • Raised troponin

  • ECG abnormalities

Exam insight: Viral myocarditis often presents in young patients with no cardiovascular risk factors.

3. Autoimmune and immune-mediated causes

These are less common but highly testable.

Associated conditions:

  • Systemic lupus erythematosus (SLE)

  • Rheumatoid arthritis

  • Sarcoidosis

  • Giant cell myocarditis (severe, rapidly progressive)

Hypersensitivity myocarditis:

  • Drug-induced (e.g., penicillins, sulfonamides, anticonvulsants)

  • Often associated with eosinophilia and rash

Key distinction: Autoimmune myocarditis may occur without a preceding viral illness.

4. Clinical features

Myocarditis has a broad spectrum of presentations, making it a favourite MRCP topic.

Three key presentations:

  1. Chest pain syndrome (mimics MI)

  2. Heart failure (dyspnoea, fatigue, oedema)

  3. Arrhythmias (palpitations, syncope)

Additional features:

  • Fever

  • Myalgia

  • Signs of cardiogenic shock (in severe cases)

5. Investigations

Investigation

Findings

Exam Tip

ECG

ST elevation, T-wave inversion

Mimics ACS

Troponin

Elevated

Not specific

Echocardiography

LV dysfunction

Useful screening

Cardiac MRI

Oedema, fibrosis

Best test

Coronary angiography

Normal coronaries

Key differentiator

Key concept: Cardiac MRI is now the investigation of choice for suspected myocarditis.

6. Management

Management is primarily supportive, as there is no universal targeted therapy.

Core principles:

  • Treat heart failure (ACE inhibitors, beta-blockers)

  • Manage arrhythmias

  • Restrict physical activity

Special cases:

  • Immunosuppressants for autoimmune myocarditis

  • Mechanical support in severe cases (e.g., ECMO)

7. Prognosis

  • Many patients recover fully

  • Some develop dilated cardiomyopathy

  • Fulminant myocarditis can be severe but reversible

8. High-yield summary (must-know points)

  1. Coxsackie B is the most tested cause

  2. Viral prodrome precedes symptoms

  3. Chest pain + raised troponin = key clue

  4. ECG mimics MI

  5. Coronary angiography is normal

  6. Cardiac MRI is diagnostic

  7. Supportive treatment is standard

  8. Risk of dilated cardiomyopathy

  9. Autoimmune causes include SLE and sarcoidosis

  10. Hypersensitivity myocarditis → eosinophilia


Practical examples / mini-cases

MCQ:

A 30-year-old man presents with chest pain following a recent viral illness. Troponin is elevated. ECG shows ST elevation. Coronary angiography is normal.

What is the most likely diagnosis?

A. Acute myocardial infarctionB. MyocarditisC. PericarditisD. Pulmonary embolism

Answer: B. Myocarditis

Explanation: The key triad—viral prodrome, elevated troponin, and normal coronaries—strongly suggests myocarditis.


Common pitfalls (5 bullets)

  • Misdiagnosing myocarditis as myocardial infarction

  • Assuming normal ECG excludes myocarditis

  • Forgetting autoimmune causes

  • Overusing biopsy in exam answers

  • Missing long-term complication (dilated cardiomyopathy)

Medical student studying cardiology notes with ECG sheets and textbooks

FAQs

1. How is myocarditis different from myocardial infarction?

Myocarditis often follows a viral illness and shows normal coronary arteries, whereas MI involves coronary artery occlusion.

2. What is the most common cause of myocarditis?

Viral infection, particularly Coxsackie B virus, is the most common and most tested cause.

3. What is the best diagnostic test?

Cardiac MRI is the preferred non-invasive investigation.

4. Is biopsy required for diagnosis?

No, biopsy is rarely required and reserved for severe or unclear cases.

5. What is the main complication of myocarditis?

Progression to dilated cardiomyopathy is the most important long-term complication.


Ready to start?

Consolidate your understanding of myocarditis and other high-yield cardiology topics with targeted revision. Practise exam-style questions using the Free MRCP MCQs or simulate real exam conditions with a Start a mock test. For structured learning, explore our MRCP lectures.


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