What is syphilis: pathogenesis and morphology

What is syphilis: pathogenesis and morphology

Syphilis is a systemic infection caused by the spirochete Treponema pallidium, which is transmitted mainly by direct sexual intercourse (venereal syphilis) and less commonly via placenta (congenital syphilis) or by accidental inoculation from the infectious materials. T. Pallidum spirochetes cannot be cultured but are detected by silver stains, dark field examination and immunofluorescence technique.

What is syphilis: pathogenesis and morphology


The organism is delicate and susceptible to drying and does not survive long outside the body. The organism invades mucosa directly possibly aided by surface abrasions following intercourse with an infected person, a primary lesion, an ulcer known as the chancre, develops at the site of infection usually the external genetalia but also lips and anorectal region. Within hours, the T. pallidum pass to regional lymph nodes and gain access tosystemic circulations. Thereafter, the disease is unpredictable. Its incubation period is about 3 weeks.

Whatever the stage of the disease and location of the lesions the histologic hallmarks of syphilis are obliterative endarteritis and plasma cell rich mononuclear cell infiltrates. The endarteritis is secondary to the binding of spirochetes to endothelial cells mediated by fibronectin molecules bound to the surface of the spirochetes. The mononuclear infiltrates are immunologic response. Host humeral and cellular immune responses may prevent the formation of chancre on subsequent infections with T. pallidum but are insufficient to clear the spirochetes.

Morphology: Syphilis is classified into three stages

Primary syphilis (chancre)

Chancre appears as a hard, erythematous, firm; painless slightly elevated papule on nodule with regional lymph nodes enlargements. Common sites are Prepuce / scrotum in men-70%, Vulva or cervix in females -50%. The chancre may last 3-12 weeks. Patients with primary syphilis who stayed for more than two week cannot be reinfected by a challenge.

Secondary syphilis

Almost any organ is involved (great mimickery). Widespread mucocutaneous lesions involving the oral cavity, plams of the hands and soles of the feet characterize it. There are also generalized lymphadenopathies mucosal patches (snail track ulcers) on the pharynx and genitalia, which is highly infectious.

Condylomatalata: which is papular lesions in moist areas such as axillae, perineum, vulva and scrotum, which are stuffed with abundant spirochetes.

Follicular syphilitidis: Small papulary lesion around hair follicules that cause loss of hair.

Nummular syphilitidis: It is coin-like lesions involving the face and perineum. Generalized lymphadenopathy and the uncommon swelling of epithrochlear lymph nodes have long been associated with syphilis. Though, asymptomatic, if untreated, secondary syphilis can relapse (latent syphilis) and more episodes of relapses may show a more granulomatous histology in skin lesions and progress to the next stage.

Tertiary syphilis

The three basic forms of tertiary syphilis are

1. Syphilitic gummas

There are grey white rubbery masses of variable sizes. They occur in most organs but in skin, subcutaneous tissue, bone, Joints and testis. In the liver, scarring as a result of gummas may cause a distinctive hepatic lesion known as heparlobatum. Collapse of the bridge of the nose and palate can occur with perforation. Osteitis and periosteitis may lead to thickening and deformity of long bones such as the sabre tibia. Histologically, gummas look like a central coagulative necrosis characterized by peripheral granumatous responses. The Trepanosomas are scanty in these gummas and difficult to demonstrate.

2. Cardiovascular syphilis

This is most common manifestation of tertiary syphilis. The lesions include aortitis, aortic value regurgitation, aortic aneurysm, and coronary artery ostia stenosis. The proximal aorta affected shows a tree -barking appearance as a result of medial scarring and secondary atherosclerosis. Endartereritis and periaortitis of the vasa vasoum in the wall of the aorta, is responsible for aortic lesions and in time, this may dilate and form aneurysm and eventually rupture classically in the arch.

3. Neurosyphilis:

Occurs in about 10% of untreated patients. The neurosyphllis comprises of i. Meningiovascular syphilis – particularly in base of brain

ii. General PARESIS of insane it affects the cerebral artery with grey matter with subsequent atrophy.

iii. Tabes dorsalis – Result of damage by the spirochetes to the sensory nerves in the dorsal roots resulting in locomotion ataxia, Charcots joint, lighting pain and absence of deep tendon reflexes

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