A 30-year-old woman presents with migratory arthralgias and has a positive antistreptolysin O titer. What is the likely diagnosis?

The presentation of migratory arthralgias along with a positive antistreptolysin O (ASO) titer strongly suggests a diagnosis of rheumatic fever. This condition is a complication that can arise following a streptococcal infection, particularly pharyngitis caused by Streptococcus pyogenes. The ASO titer serves as a serological marker indicating recent streptococcal infection, which is pivotal in identifying rheumatic fever.

In rheumatic fever, migrating joint pain is a classic symptom, often affecting larger joints in succession, which aligns with the migratory nature of the arthralgias described. The condition is also associated with other clinical findings such as carditis, erythema marginatum, and Sydenham chorea, but the combination of migratory arthralgia and elevated ASO titer is particularly indicative.

In contrast, reactive arthritis typically occurs following an infection elsewhere in the body, not necessarily with a direct association to streptococcal infection, and would not usually present with an elevated ASO titer. Gout is characterized by sudden onset of pain in specific joints due to uric acid crystal deposition and does not correlate with such serological markers. Psoriatic arthritis,