Patient outcome and follow-up
A quantitative rapid plasma reagin (RPR) test was performed with a titer of 1/64 and a fluorescent treponemal antibody absorption test showed a positive result. Serology could be consistent with a new infection, inadequate treatment before infection or expected serologic findings post-treatment.
Pathological examination of tibia lesions showed unspecific inflammatory cells and no evidence of malignancy. Immunohistochemical stain demonstrated no treponema.
The patient was treated empirically with intravenous penicillin for two weeks and on-demand analgesics. No additional treatment was performed. Symptomatic relief occurred rapidly after the start of the antibiotic. Follow-up PET-CT showed markedly decreased uptake of the bone lesions. The antibody titer significantly diminished (1/16) and the finger fracture healed 11 months later.
Background
Syphilis is a sexually transmitted disease caused by the spirochete Treponema pallidum. Musculoskeletal manifestations can be associated with congenital, secondary, and tertiary syphilis. However, although bone involvement is a common finding in congenital syphilis, it is rare in secondary syphilis [1].
Reynolds and Wasserman review the largest series of early acquired syphilis in 1942. They found only 15 cases with bone involvement of 10000 cases of early acquired syphilis (0.15%) [2].
A recent English- language literature review from 1964 to 2013 found 36 cases of secondary syphilis with bone involvement [3]. In this review, the diagnosis of early syphilis was suspected based on mucocutaneous findings in 76% of patients. In the remaining 24% of the patients there was no history of syphilitic mucocutaneous lesions, and high-titer nontreponemal serologic tests were the only evidence of early syphilis, as in our case. The most frequent skeletal involvement was in the long bones of the limbs and the skull [3].
Bone pain was the most common complaint. Examination may reveal tenderness over the involved bones and local oedema.
Bone involvement is usually in the form of proliferative periosteal reaction and, less frequently, destructive osteitis and osteomyelitis. Lytic lesions, mainly in the long bones, and aggressive periosteal reaction surrounding the lesion are typical findings [1,2,3,4]. Scintigraphy may show polyostotic uptake that can mimic malignancy [5]. Imaging is important both in the diagnosis and in the assessment of response to treatment. Pathologic examination usually reveals non-specific inflammatory infiltration. Identification of spirochetes in the bone lesion with dark-field microscope, silver stain, immuoperoxidase stain, or polymerase chain reaction is uncommon, and only 5 cases have been reported in the English literature [3].
The availability of imaging modalities such as CT, MRI, and bone scintigraphy has led to easier diagnosis and more frequent reporting of osseous syphilis than in the past [4]. Imaging can detect silent or even asymptomatic bone lesions.
Syphilis is a treatable disease with antibiotics [6]. Untreated, it may lead to severe disease [5].
It appears that the incidence of bony involvement in early syphilis may be higher than previously thought [3,4,5]. It is important to keep in mind this diagnosis, since the imaging appearance may mimic other diseases such as malignancy.
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