Syphilis is a common sexually transmitted disease which, if left untreated, can result in a multiorgan infection. The causative organism is the spirochaete (from the Greek ‘spiral hairs’) Treponema pallidum. Other subspecies cause similar diseases such as yaws and pinta but these tend to be less severe and do not cause multisystem morbidity. Syphilis is a classic biphasic illness characterised by an initial skin infection which may be followed years later by involvement of the central nervous system (CNS), skeletal and cardiovascular systems with the great vessel the aorta at particular risk. Congenital transmission can occur and a range of clinical features can afflict the baby. Severe deformities, and even intrauterine death, are associated with transmission late in the pregnancy. Early and appropriate antimicrobial treatment of syphilis in all its guises is therefore of critical importance. Newer imaging techniques have become a useful adjunct in aiding diagnosis, which still relies heavily on serological assays and clinical acumen.

Key Concepts:

• Enhancement of infectivity of syphilis and of early syphilitic lesions, in patients with concomitant HIV.
  
• The relapsing nature of syphilis, both in early stages and in the late congenital disease, as in interstitial keratitis and Clutton's joints.
  
• Primary form of syphilis is an early localised primary lesion. The secondary phase is manifested by a systemic disease, whereas the later stages are again localised.
  
• Similarly, early congenital lesions tend to be disseminated, whereas late lesions are localised.
  
• Newer imaging techniques are useful both in diagnosis and for monitoring treatment, especially in those patients with brain and cardiovascular syphilis.