Late Latent ("Hidden") Syphilis

Essentials of Diagnosis

• No physical signs.
• History of syphilis with inadequate treatment.
• Positive serologic tests for syphilis.

General Considerations & Treatment

Latent syphilis is the clinically quiescent phase during the interval after the disappearance of secondary lesions and before the appearance of tertiary symptoms. Early latency is defined as the first year after infection, during which time most infectious lesions recur ("relapsing syphilis"); after the first year, the patient is said to be in the late latent phase. Transmission to the fetus, however, can probably occur in any phase. There are (by definition) no clinical manifestations during the latent phase, and the only significant laboratory findings are positive serologic tests. A diagnosis of latent syphilis is justified only when the cerebrospinal fluid is entirely negative, x-ray and physical examination show no evidence of cardiovascular involvement, and false-positive tests for syphilis have been ruled out. The latent phase may last from months to a lifetime.

It is important to differentiate latent syphilis from a false-positive serologic test for syphilis, which can be due to the many causes listed above.

Treatment of late latent syphilis or latent syphilis of unknown duration is with benzathine penicillin G, 2.4 million units three times at 7-day intervals (total dose: 7.2 million units). The only alternative to penicillin for therapy of late latent syphilis is doxycycline, 100 mg twice daily, or tetracycline, 500 mg four times a day, both for 28 days. If there is evidence of central nervous system involvement, a lumbar puncture should be performed and, if positive, the patient should receive treatment as for neurosyphilis. Only a small percentage of serologic tests will be appreciably altered by treatment with penicillin. The treatment of this stage of the disease is intended to prevent the late sequelae.