Differential Diagnosis
- Single most likely diagnosis
- A. Drug-induced lupus erythematosus: This is the most likely diagnosis given the patient's history of taking phenytoin, which is known to induce lupus-like symptoms in some individuals. The presence of anti-histone antibodies, which are more commonly associated with drug-induced lupus than systemic lupus erythematosus, further supports this diagnosis.
- Other Likely diagnoses
- B. Systemic lupus erythematosus: Although less likely than drug-induced lupus given the context of phenytoin use, systemic lupus erythematosus (SLE) is still a possibility, especially with the positive ANA and ssDNA antibodies. However, SLE typically presents with a broader range of autoantibodies and more diverse clinical manifestations.
- Do Not Miss
- C. Purple glove syndrome: This is a rare but serious condition associated with intravenous phenytoin administration, characterized by discoloration and swelling of the limb where the drug was administered. Although the patient's symptoms do not directly suggest this condition, it's crucial to consider due to the potential severity and the fact that the patient is on phenytoin.
- Infections or sepsis: Given the patient's presentation with fever and fatigue, it's essential to rule out infections or sepsis, which could be life-threatening if not promptly addressed.
- Rare diagnoses
- D. Rheumatoid arthritis: While rheumatoid arthritis can cause joint pain and fever, the presence of specific autoantibodies like ssDNA and ANA, along with the patient's use of phenytoin, makes this diagnosis less likely in this context.
- Other autoimmune or rheumatologic conditions: Conditions like mixed connective tissue disease or scleroderma could be considered but are less likely given the information provided and the presence of drug-induced lupus risk factors.