Syphilis causing elevation of anti-CCP: a case report of medical mimicry

Infection with Treponema pallidum, or syphilis, is often called the "Great Imitator" because of its propensity for atypical presentations and non-specific symptoms. In addition, syphilis has been shown to create false-positive results for common tests, including Lyme disease, HIV, and multiple autoimmune conditions. One that has not been documented is anti-cyclic citrullinated peptide (anti-CCP). Anti-CCP is a highly specific test for Rheumatoid Arthritis. However, in this case, syphilis led to false-elevations in anti-CCP.

A 29-year-old G5P3 female presented to the emergency department with a 3-month history of progressive rash, night sweats, chills, lymphadenopathy, dysphagia, headache, and arthralgia. Work-up included a positive CMV test and elevated C-reactive protein and Erythrocyte Sedimentation Rate. Remaining tests were normal, and she was treated symptomatically for CMV. Eventually, her dysphagia progressed to an inability to tolerate liquids, prompting hospitalization. Examination showed a diffuse rash, including the palms and soles, and painful lymphadenopathy. Laboratory testing revealed positive rapid plasma reagin, confirmed by a treponemal antibody study. She was initially treated with doxycycline due to penicillin shortages, with plans to receive penicillin at the health department. However, she returned four days later with neurological symptoms and results positive for neurosyphilis and was successfully treated with a 14-day course of intravenous penicillin. During her first admission, results were positive for anti-CCP and antinuclear antibodies (ANA), suggesting a rheumatologic etiology. Six months later, follow-up studies showed resolution, suggesting syphilis caused the elevations.

Secondary syphilis is typically associated with the elevation of certain autoimmune markers; however, anti-CCP is not commonly among them. This particular case is notable due to the elevated anti-CCP level observed in the absence of any rheumatologic disease. In alignment with the majority of secondary syphilis cases, the patient presented with significant joint pain and swelling as the primary symptoms. This clinical manifestation, coupled with positive ANA and anti-CCP results, could easily result in a misdiagnosis of rheumatoid arthritis. If left untreated, syphilis may advance to neurosyphilis, leading to severe complications. This case is significant as it underscores a novel instance of medical mimicry in secondary syphilis, which clinicians must be able to identify.