20th February 2025

A 57-year-old woman presents to the emergency department with a 4-day history of increased shortness of breath, cough and pleuritic chest pain.

A 57-year-old woman presents to the emergency department with a 4-day history of increased shortness of breath, cough and pleuritic chest pain. There is no haemoptysis or leg swelling. 

Her past medical history includes hypothyroidism and systemic lupus erythematous. Her medication is comprised of levothyroxine and hydroxychloroquine. She has no allergies.

On examination there are fine crackles throughout the chest and an erythematous rash on her face. She is euvolemic.

Obs: Sats 90% on 60% O2, HR 100 bpm, BP 110/75 mmHg, T 37.7 degrees Celsius, RR 28/minute.

Her ABG shows: pH 7.5, pCO2 3.2, pO2 8.7, HCO3 25, Lactate 1.2

Blood tests are as follows:

Hb 120 g/L (M 130-180 g/L; F 115-165 g/L), WCC 7×10⁹ /L (4-11×10⁹ /L), Plt 300×10⁹ /L (150-450×10⁹ /L), renal function unremarkable, CRP 30 mg/L (<5 mg/L). NT-proBNP 100 pg/mL (<75 years: <125 pg/mL; > 75 years: <450 pg/mL).

CXR reveals widespread infiltrates. Both extended respiratory viral swab and repeated sputum samples (including screening for atypical pneumonia) are negative. 

What is the most likely diagnosis?

Select the SINGLE most appropriate option from the list below. Select ONE option only.