LATENT SYPHILIS

By

Major M. P. Vora, M.B.B.S., D.V.D., I.M.S. (Rtd.)

Hon. Senior Venereologist, St. George’s Hospital, Bombay

Indian Medical Record

A monthly journal of Public Health, Tropical Medicine and Surgery etc .

Volume LXXXVI, Number 10, of October 1966

Pages 153-156

This article was solely contributed to Indian Medical Record

Syphilis is generalised at first, subsequently localised and dispersed. After inoculation in the body, Treponema pallida enters lymphatics multiply and reach all tissues of the body through the blood stream. Generalisation of infection occurs in about 2 to 3 days, well in advance of the appearance of the primary lesion, chancre. Some Treponema pallida escape from circulation and initiate metastatic lesions in and around the vessels and some tissues especially of ectodermal origin. After a variable period of generalisation, the spirochaetes disappear from the blood stream and surface lesions and the process of resolution begins. Thus syphilis is characterised by repeated episodes of spirochaetemia, metastatic lesions and resolution till the immune forces of the host have attained maximum effectiveness or immunity i.e. two to five years. The development of refractoriness to dissemination of the organisms is disturbed by administration of subcuartive or irregular antisyphilitic therapy in the early stages of syphilis. Hence the dangers of inadequate or irregular treatment of early syphilis will be apparent. Involvement of cardiovascular or nervous system is more frequent in inadequately treated early syphilis than in syphilis which receives no treatment at all or which receives adequate and regular treatment during its early stages.

The process of resolution goes on to completion in a small proportion of cases ending in “biologic cure”; while in large proportion on the contrary, one or more foci persist in various locations. If the presence of these foci is hidden beyond diagnostic reach, the state of infection is called “latent”. If the patient has an obvious lesion of syphilis such as gumma, optic atrophy, rash then the patient cannot be regarded as having latent syphilis. Thus the term latent syphilis is limited to the presence but not he location of syphilitic foci. The presence of foci in the central nervous system is not hidden beyond diagnostic reach; it can be detected by examining the cerebrospinal fluid. Therefore, unless the C.S.F. has been shown normal, the patient cannot be regarded as having latent or inapparent syphilis. If the evidence of syphilitic infection is present in the C.S.F. and there are no clinical signs or symptoms, the stge of the disease is called asymptomatic neurosyphilis. Very often metastatic lesions in the aorta can remain hidden beyond diagnostic reach for a long period. Uncomplicated syphilitic aortitis is often without physical signs and is extremely difficult to diagnose with accuracy with all the procedures of examination at one’s disposal. Though presence of neurosyphilis or cardiovascular syphilis does not become clinically evident for many years, the initial infection or the process of metastatic lesions in these systems begins during the period of early spirochaetemia.

As surface lesions are absent, the individual with latent syphilis cannot transmit the infection at this stage. However, as recurrent generalisation of the infection may occur at any time until the forces of resistance have fully developed i.e. 2-5 years; such an individual is liable to the development of metastatic lesions. The later may or may not be infectious depending on the duration of the infection and whether the surface of the body is involved. Until the possibility of redissemination of infection has been remote, the prognosis and the principles of therapy of either latent or infectious syphilis are identical.

It has been found convenient to subdivide the latent syphilis into early and late at a point of about two to four years after the onset of infection. This line of division is arbitory and based on assumption that there would be no recurrent episodes of spirochaetemia after this period. There is no unanimity of opinion among venereologists as to the exact duration of infection which can be termed early latent. Some like to restrict the term to the infection of 2 years’ duration while others prefer it to the infection upto four years’ duration for various reasons. The early latent syphilis may return to the metastatic or infectious variety at any time. Once the localization of the process becomes stabilised, the disease enters into the stage of late latent syphilis.

Once the stage of late latency has been reached, the infection may pursue any of these possible courses.

• the foci still present after resolution of infectious lesions may slowly heal over a period of years with complete eradication of the organisms i.e. “biologic cure”. This process is observed in about one-fifth of the cases.

• the foci of infection persist throughout the life of the host but evoke minimal reaction so that the health of the infected person remains unimpaired, “healthy carrier”.

• The foci progress at slow and inconsistent rate until sufficient tissue reaction has occurred to procure clinical evidence of the disease. The resultant clinical disease may be fatal or benign, depending on the amount of damage and the structures affected. Most of the fatalities occur as the result of cardiovascular or nervous syphilis. There is very chancre that an individual with late latent syphilis (the C.S.F. being normal and duration being over four years) will subsequently develop neurosyphilis, however, an individual with neurosyphilis may eventually develop clinically demonstrable lesions in other areas of the body.

Since penicillin is now used for a number of diseases, and due care is rarely taken in every case to have an adequate inquiry and a sample of blood for the S.T.S. before administration of penicillin which is likely to mask early syphilis, the incidence of latent syphilis has gone up lately. In fact a large number of syphilitics are masked in the early stages, making early detection of infection clinically a difficult problem. Approximately 70 to 80% of the syphilitics seen by the general practitioner are in this stage of disease; it is therefore very important to understandits clinical entity. Many patients with late latent syphilis are either over-treated or neglected. Once true latency has been established, the subsequent course of the infection is usually benign in the majority of the cases. It is important therefore, that this frequently encountered benign form of syphilis be clearly distinguished from potentially serious types of infection, which require vastly different forms of therapy.

In late latent syphilis, the patient has undoubted serologic positivity and historical evidence of syphilis of more than two or four years’ duration, but in whom no clinical evidence of syphilitic disease or focus is detected by :-

• the complete physical examination

• the neurologic examination

• the C.S.F. examination

• the examination of eye grounds

• Roentgenologic examination of the heart, aorta and bones.

Unless these criteria are met with, it is possible to overlook detectable and potentially serious syphilitic infection. It is therefore necessary that a physician should obtain information made available by these procedures as quickly as possible. To establish the latency of a syphilitic infection presents no formidable difficulties; however, it is difficult at times to prove that the infection is more than four years’ duration. Complete history, date of exposure, appearance of the primary lesion, date of the S.T.S. and treatment will be of help. In the absence of such an evidence, a physician has to use his own judgment as to whether the latent infection is old or recent. It is advisable to regard syphilis of unknown duration in a young person as a recently acquired infection.

Treatment

The early latent syphilis for all practical pruposes should be treated in the same way as early active or infectious syphilis which needs an average dose of 6.m.u. of procain penicillin G in ten days. The response and prognosis are very good.

Once the true late latency has been established, there are no need theoretically for the administration of antisyphilitic treatment. Unfortunately, there is no way in which apparently latent syphilis can be distinguished from the active disease of the aorta or other viscera, which is not progressed to a point of clinical recognition. Thus a physician has no choice other than to treat all individuals with late latent syphilis. An average dose of 9 to 12 m.u. of procain penicillin G in 15 to 20 days is considered adequate for this stage of infection. Since these patients exhibit no clinical evidence of infection, they will show no change in clinical status as the result of successful therapy. A precise evaluation of the results obtains can only be made by following the patient throughout his or her life. About 2% of the cases of late latent syphilis who are treated will subsequently develop serious manifestations of late syphilis and show evidence of progression despite an adequate treatment especially in the older age group. Experience shows that prolongation of treatment does not help to eliminate this small chance of progression in small per cent of late latent cases of syphilis.

Serology

In late syphilis, serologic tests for syphilis do not reverse to normal readily after treatment. About 50% of the cases will show either serologic reversal or pronounced fall in the titre by the end of a year or so, after the completion of treatment. In a small proportion of cases, the titre gets stabilised at a level and remains unchanged for years after the therapy. This frequent failure of the serologic tests for syphilis to reverse to normal after treatment to of late latent syphilis is called sero-resistance. This phenomenon of sero-resistance, which is observed in late latent syphilitic infection, must not be confused with the persistently positive serologic tests in the individual with obvious progressive lesions of the aorta or nervous system. The later cannot be considered as an example of sero-resistance. Two important facts concerning sero-resistance needs to be understood properly. (1) the phenomenon of sero-resistance does not alter the ultimate outcome of the treated infection in anyway. (2) the sero-resistance can not be influenced by additional antisyphilitic or non-specific treatment. Hence it is irrational & futile to continue therapy in such cases. Once the serologic tests for syphilis have been repeatedly negative in an individual with late latent syphilis, subsequent true serologic relapse seldom occurs.

The Cerebrospinal fluid :-

The C.S.F. is examined as a routine before the institution of treatment in early and late latent syphilis; for, the normal C.S.F. is the pre-requisite for the diagnosis of latency. In case the latent infection is more than four years’ duration, and the first examination of the C.S.F. is found to show normality of the fluid, subsequent examination of the C.S.F. is not necessary. Where it is not possible to determine the duration of the infection or the possibility of early latent syphilis can not be excluded, the C.S.F. should be re-examined 18 to 24 months after the institution of antisyphilitic therapy, as is done after the treatment of early active syphilis or early latent syphilis. If the C.S.F. shows at the 1 st examination changes or abnormalities suggestive of neurosyphilis, subsequent examinations of the C.S.F. on one or more occasions become necessary to find out the response to the antisyphilitic treatment. The total cell count and protein estimation are the earliest and most reliable indices of the successful therapy of neurosyphilis. The T.P.I and FTA-ABS tests are of little value as an index of therapeutic response.

A fact which is forgotten too often in the treatment of syphilis is that an adequate treatment of latent syphilis does not mean “cure” unless the results of repeated physical examinations, serologic responses and the C.S>F. studies over a considerable period confirm it. Then and then alone its permanency could be certain.