MRCP Part 1 Infectious Diseases and Immunology 2

Question 1

A 35-year-old woman presents with fever, arthralgia, and a malar (butterfly) rash. Blood tests show pancytopaenia, raised anti-dsDNA antibodies, and low complement C3 and C4. What is the most likely diagnosis?

Accepted Answer

Systemic lupus erythematosus (SLE)

Answer

SLE characteristically presents in young women with multi-system involvement including malar rash, arthralgia, cytopaenias, and renal disease. Anti-dsDNA antibodies are highly specific for SLE and correlate with disease activity, particularly lupus nephritis. Low complement levels indicate active immune complex consumption.

Question 2

A renal transplant recipient on ciclosporin, mycophenolate, and prednisolone develops fever and a CT chest shows ground-glass opacification. Bronchoalveolar lavage with silver staining reveals cysts. What is the causative organism?

Accepted Answer

Pneumocystis jirovecii

Answer

Pneumocystis jirovecii pneumonia (PJP) typically presents in immunosuppressed patients with progressive dyspnoea, dry cough, and fever. CT shows bilateral ground-glass opacification. Diagnosis is confirmed by identifying cysts on silver staining of BAL fluid. Treatment is high-dose co-trimoxazole, with adjunctive steroids if hypoxic.

Question 3

A 40-year-old man presents with recurrent sinopulmonary infections and chronic diarrhoea. Serum immunoglobulins show very low IgG, IgA, and IgM. B-cell numbers are markedly reduced. What is the most likely diagnosis?

Accepted Answer

Common variable immunodeficiency (CVID)

Answer

Common variable immunodeficiency (CVID) is the most common symptomatic primary antibody deficiency in adults, presenting with recurrent infections and low immunoglobulin levels. Unlike X-linked agammaglobulinaemia (which presents in infancy with absent B cells), CVID typically presents in the second or third decade with reduced but not absent B cells.

Question 4

A patient returns from South-East Asia with cyclical fevers every 48 hours, rigors, and splenomegaly. Blood film shows ring forms and banana-shaped gametocytes within red blood cells. Which species of Plasmodium is responsible?

Accepted Answer

Plasmodium falciparum

Answer

Banana-shaped (crescent) gametocytes are pathognomonic of Plasmodium falciparum. While P. falciparum classically causes irregular fevers rather than strict 48-hour cycles, it can produce tertian periodicity. P. falciparum is the most dangerous species, capable of causing cerebral malaria, severe anaemia, and multi-organ failure.

Question 5

A 25-year-old man presents with a 2-week history of productive cough, night sweats, and weight loss after returning from India. Sputum AFB smear is positive. He lives with his partner and 2-year-old child. What is the most important public health action?

Accepted Answer

Contact tracing and screening of household contacts

Answer

Active pulmonary TB is notifiable, and contact tracing is the most important public health intervention. Household contacts, especially children under 5, are at highest risk. Contacts should be screened with symptom assessment, chest X-ray, and interferon-gamma release assay (IGRA). The child may need chemoprophylaxis regardless of screening results due to young age.

MRCP Part 1 Practice Test

MRCP Part 1 Practice Test

MRCP Part 1 Infectious Diseases and Immunology 2