From the clinical aspect

• MTX-pneumonitis: typically has an acute or subacute onset, often within the first few months of treatment, and is considered a hypersensitivity reaction. RA-ILD, on the other hand, usually develops insidiously.
• RA-ILD: Typically has a more gradual, insidious onset with symptoms like exertional dyspnea, cough, and fatigue. It can also present with digital clubbing or Velcro-like crackles on auscultation.
• PJP: Presents with fever, cough, and dyspnea, often with hypoxemia. In immunocompromised individuals, it can progress rapidly.

HRCT findings can also be of benefit:

• MTX-pneumonitis may show ground-glass opacities and a hypersensitivity pneumonitis pattern.
• RA-ILD may present with usual interstitial pneumonia (UIP) or non-specific interstitial pneumonia (NSIP) patterns.
• PJP often shows ground-glass opacities and consolidations.