A 77-year-old man has had progressive dementia and gait ataxia for the past 9 years. He succumbs to bronchopneumonia. Autopsy shows that the thoracic aorta has a dilated root and arch, giving the intimal surface a "tree-bark" appearance. The microscopic examination of the aorta shows an obliterative endarteritis of the vasa vasorum. Which of the following laboratory findings is most likely to be recorded in this patient's medical history?

This description is most suggestive of syphilitic aortitis, a complication of tertiary syphilis, with characteristic involvement of the thoracic aorta. The history also suggests tabes dorsalis and neurosyphilis. Obliterative endarteritis is not a feature of other forms of vasculitis. High-titer double-stranded DNA antibodies are diagnostic of systemic lupus erythematosus, and the test result for P-ANCA (antibodies mainly directed at myeloperoxidase) is positive in various vasculitides, including microscopic polyangiitis. Ketonuria can occur in individuals with diabetic ketoacidosis. A high sedimentation rate is a nonspecific marker of inflammatory diseases.