Nationwide statistics for syphilis are most important for early syphilis (primary and secondary) because these represent the recently acquired (incident) cases, and the cases that are most infectious. Primary and secondary syphilis are relatively uncommon in older adults, with only 4% of the cases in the U.S. occurring in persons aged 55 yr and older during 1997 (8). Nationwide efforts for syphilis elimination have led to dramatic declines in syphilis rates in all age groups, but between 1996 and 1997, the rates in persons aged 55 and older decreased only slightly. Regardless of age group, early syphilis is highly infectious, with an estimated 30-60% chance of acquiring infection after a single sexual contact (9). In older women, the risk may be higher due to vaginal thinning in the postmenopausal state leading to more abrasions during sexual intercourse. Syphilis should be considered in the differential of any new genital ulceration, especially if the ulceration is painless, or for unexplained skin rash in a sexually active patient.
The diagnosis of syphilis in the elderly may be challenging for several reasons. First, the prevalence of false-positive nontreponemal serologies, such as the rapid plasma reagin (RPR) or venereal disease research laboratory (VDRL), in the elderly is increased. In all age groups, it is necessary to confirm a positive nontreponemal test result with a treponemal-specific serology, such as the microhemagglutination Tre-ponemapallidum (MHA-TP) or fluorescent treponemal antibody absorbed (FTA-ABS), prior to considering treatment (note: the MHA-TP will be replaced shortly by a new, recently FDA-approved test called the T. pallidum-particle agglutination, or TP-PA, which is produced by the manufacturer of the MHA-TP). Second, in patients who have untreated syphilis for many years and are presenting with late complications, the RPR and VDRL may be negative, with only a positive treponemal serology as indication of infection. Therefore, the possibility of either false-positive or false-negative screening nontreponemal tests exists in the elderly. Finally, since the elderly have many intercurrent illnesses and are not perceived by medical providers as being sexually active or at risk for syphilis, symptoms or signs of syphilis may be mistaken for other disease states, such as a drug reaction, urinary tract infection, or benign perineal ulceration.
Whereas early syphilis is uncommon in the elderly, latent syphilis is a more frequently encountered problem. A serum RPR is a routine test to perform in the evaluation of dementia, so a common dilemma is how to determine the significance of a positive RPR. If the confirmatory test is positive, then the clinician must decide if the patient requires evaluation for neurosyphilis. According to the 1998 CDC STD Treatment Guidelines (10), cerebrospinal fluid (CSF) evaluation is recommended if the patient has any of the following: (1) neurologic, auditory or ophthalmologic symptoms or signs suggestive of syphilis, such as uveitis, interstitial keratitis, cranial nerve palsies, meningitis, or cerebrovascular accident, which usually occur months to a few years after infection, or tabes dorsalis, general paresis, or psychological or behavioral changes that usually occur many years after infection; (2) suspected treatment failure or relapse of previously known syphilis, demonstrated by a failure to display a fourfold drop in the RPR (or VDRL) titer, or presence of an increase in titer; (3) co-infection with HIV and syphilis of greater than 1 yr duration; or (4) active signs of other forms of tertiary syphilis (aortitis, gummas). Routine lumbar puncture for infection of greater than 1 yr duration or for planned nonpenicillin therapy is not routinely recommended. If the patient undergoes a lumbar puncture, then a second problem that the clinician may encounter is interpreting the CSF analysis. There is no one test that is 100% sensitive for the diagnosis of neurosyphilis. In a patient with positive serum syphilis serology, if the CSF VDRL is positive (without significant contamination of the CSF with blood), most experts would agree that the patient has neurosyphilis. However, in patients with negative CSF VDRL, the clinician should consider treatment if there is any abnormality of the CSF, especially a pleocytosis of >5 white blood cells (WBC)/mm3, even though this finding is not specific for neurosyphilis. It is important to recognize, however, that the protein level in the CSF may increase with age and other associated conditions, thus the interpretation of the CSF profile with a slightly elevated protein level as the sole abnormal finding may be difficult. Although the FTA-ABS is not a recommended test to perform on CSF because of problems with specificity, a negative CSF FTA-ABS suggests that neurosyphilis is unlikely in these cases (11).
The recommended treatment of syphilis has not changed significantly. Syphilis of less than 1 yr duration (primary, secondary, and early latent) is treated with a single injection of benzathine penicillin, 2.4 million units (MU) intramuscularly (i.m.), and syphilis of more than 1 yr duration (late latent and tertiary) is treated with weekly injections of intramuscularly administered benzathine penicillin, 2.4 MU for 3 wk. The treatment of neurosyphilis is best accomplished with 18-24 MU of intravenous (i.v.) penicillin G for 10-14 d; this recommended dose is slightly higher than that recommended in the 1993 guidelines. An alternative regimen, which can be administered on an outpatient basis, is procaine penicillin 2.4 MU i.m. administered once a day along with probenecid 500 mg orally four times a day, both for 10-14 d (10). Many experts recommend treating patients with neurosyphilis with an additional two injections of 2.4 MU benzathine penicillin weekly immediately following the course of i.v. penicillin in order to achieve the same duration of therapy as for tertiary syphilis.
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