Differential Diagnosis

• Single most likely diagnosis
  • Adult Still's disease: The patient's presentation with fever, arthralgia, weight loss, pleuritic chest pain, and synovitis of the small joints of the hand, along with laboratory findings of elevated ESR, CRP, and ferritin, is highly suggestive of Adult Still's disease. The absence of a skin rash, nail infarction, and cardiac murmur, and the presence of a high ferritin level, further supports this diagnosis.
• Other Likely diagnoses
  • Systemic lupus erythematosus (SLE): Although the ANA titer is only slightly elevated, SLE can present with a wide range of symptoms, including fever, arthralgia, and pleuritic chest pain. However, the lack of other characteristic features, such as a skin rash or renal involvement, makes this diagnosis less likely.
  • Rheumatoid arthritis with vasculitis: The patient's presentation with synovitis of the small joints of the hand and elevated inflammatory markers could suggest rheumatoid arthritis. However, the absence of other characteristic features, such as morning stiffness or rheumatoid nodules, and the presence of systemic symptoms, makes this diagnosis less likely.
• Do Not Miss diagnoses
  • Infective endocarditis: Although the patient does not have a cardiac murmur, infective endocarditis can present with systemic symptoms, such as fever and weight loss, and can be associated with embolic phenomena, such as pleuritic chest pain. It is essential to consider this diagnosis, as it can be life-threatening if missed.
  • Lymphoma: The patient's presentation with fever, weight loss, and elevated inflammatory markers, along with a low platelet count and anemia, could suggest lymphoma. Although this diagnosis is less likely, it is essential to consider it, as it can be life-threatening if missed.
• Rare diagnoses
  • Sarcoidosis: The patient's presentation with pleuritic chest pain and elevated inflammatory markers could suggest sarcoidosis. However, the absence of other characteristic features, such as hilar lymphadenopathy or skin lesions, makes this diagnosis less likely.
  • Hemophagocytic lymphohistiocytosis (HLH): The patient's presentation with fever, weight loss, and elevated inflammatory markers, along with a low platelet count and anemia, could suggest HLH. Although this diagnosis is rare, it is essential to consider it, as it can be life-threatening if missed.