Table 2 Criteria for definite or probable methotrexate pneumonitis diagnosis

Methotrexate pneumonitis is characterized as "definite" if one of the major criteria is present in conjunction with three of the five minor criteria. "Probable" methotrexate pneumonitis is present if major criteria 2 and 3 plus two of the five minor criteria are present [43]*.

Major criteria

• Hypersensitivity pneumonitis by histopathology without evidence of pathogenic organisms

• Radiologic evidence of pulmonary interstitial or alveolar infiltrates

• Blood cultures (if febrile) and initial sputum cultures (if sputum is produced) that are negative for pathogenic organisms.

Minor criteria

• Shortness of breath for less than eight weeks

• Nonproductive cough

• Oxygen saturation ≤ 90% on room air at the time of initial evaluation

• DL_CO ≤ 70% of predicted for age

• Leukocyte count ≤ 15,000 cells/mm³.