Syphilis is a sexually transmitted infection caused by Treponema pallidum , with diverse clinical presentations. In the acquired form, in addition to cutaneous and mucosal manifestations, neurological and cardiovascular involvement may occur. Bone involvement is extremely rare, especially in patients without HIV coinfection, with few reports in the literature. In such cases, patients may present with bone pain, edema, tenderness, and local swelling. Imaging tests may reveal variable patterns such as osteolytic lesions, cortical thickening, or bone destruction. These manifestations are nonspecific and vary according to the stage of infection, potentially mimicking neoplasms, metastases, or chronic osteomyelitis, which makes diagnosis difficult. This case report describes a previously healthy 55-year-old woman who presented with left leg pain without a history of trauma. Magnetic resonance imaging (MRI) showed periosteal reaction in the tibia, initially interpreted as a stress fracture. Within a few weeks, she developed headache and frontal swelling, and an osteolytic lesion in the left frontal bone with leptomeningeal enhancement was identified on MRI. A hypothesis of neoplasia with bone metastasis was initially considered. Chest and abdominal CT scans showed nonspecific axillary and inguinal lymph nodes. Bone scintigraphy revealed areas of increased uptake in the skullcap and tibia. Serologic tests were positive for syphilis (VDRL 1:512 and FTA-ABS positive) and negative for HIV, confirming syphilis with bone involvement in an immunocompetent patient. She was treated as late syphilis with 7.2 million IU benzathine penicillin, divided into three weekly doses. Three months after treatment, she showed significant clinical improvement, with regression of swelling and pain in the skull and leg, VDRL decreased to 1:16, and MRI demonstrated reduction of bone lesions and meningeal enhancement, indicating a favorable therapeutic response. The scarcity of data in the literature suggests that bone syphilis is rare, and most cases described in recent years occurred in HIV-coinfected patients. This report reinforces the importance of considering syphilis in the differential diagnosis of unexplained bone pain or bone lesions of uncertain etiology, even in immunocompetent patients, as early recognition allows appropriate treatment and prevents bone complications.
Castro et al. (Sun,) studied this question.