AssessmentsTreponema pallidum (Syphilis)
Treponema pallidum (Syphilis)
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 47-year-old male presents to his primary care physician with worsening gait disturbance. He says, “I feel so unsteady on my feet, I can only get around in a wheelchair now.” In addition, the patient has experienced severe lancinating pain in his back. Past medical history is notable for HIV, hypertension, type II diabetes mellitus, and polysubstance abuse. His temperature is 37.0°C (98.6°F), pulse is 94/min, respirations are 12/min, blood pressure is 100/74 mmHg, and O2 saturation is 95% on room air. Neurological exam is notable for bilateral dysmetria, a positive Romberg sign, and absent deep tendon reflexes. A screening rapid plasma reagin (RPR) test is positive. Which of the following additional neurologic findings is commonly associated with this patient's condition?
Contributors:Jahnavi Narayanan, MBBS, Jake Ryan, Sam Gillespie, BSc, Sarah Clifford, BMBS, BSc (Hons), Evan Debevec-McKenney
Treponema pallidum can be considered a gram-negative bacterium although its cell envelope differs from other gram-negative bacteria.
They belong to a group of bacteria called spirochetes, which are long and thin, and contain endoflagella, which are a band of protein filaments that coil within the spirochetes, and give them a spiral shape - kind of like a curly fry, but less appetizing.
The endoflagella also help the spirochetes to move around by spinning or twisting, it’s a bit like a drill that’s slowly boring into a piece of wood.
It can also happen when people share contaminated needles, or when they have direct contact with a skin lesion on an infected person, ‘cause the lesion is covered in this fluid which is rich in spirochetes.
The second way is called congenital syphilis and it’s when a pregnant person has syphilis and Treponema pallidum infects a baby either in the uterus or while the baby exits through the vagina at birth.
In acquired syphilis, there are three stages to the infection. The first stage is called primary syphilis or the early localized stage, and it usually starts 1 to 3 weeks after the T. pallidum lands on the skin or mucous membrane.
A syphilitic chancre is painless - and you can remember that by dropping in a “u” to make it chan”cure” like you’re “cured” of the pain.
These chancres have a hard base, raised borders, and are usually covered by a fluid rich in spirochetes, and this can spread to other parts of the body as well as to other individuals.
Syphilitic chancres typically heal on their own over a few months, but during that time, some spirochetes go to nearby lymph nodes where they cause lymphadenopathy, which is lymph node enlargement, and then they get into the lymph and finally into the bloodstream.
The second stage is secondary syphilis, or the dissemination stage, and it occurs about 6 to 12 weeks after the infection.
During this stage, spirochetes enter the bloodstream, which is called spirochetemia, and this causes generalized lymphadenopathy, which is when spirochetes can be found in lymph nodes throughout the body.
The spirochetes like to attach to and infect endothelial cells in small capillaries near the skin. This causes a non-itchy maculopapular rash, which are small bumps that are either flat or raised.
The rash starts on the trunk and spreads out to the arms and legs and eventually to the palms, soles, genitalia, and other mucous membranes.
So these various rashes can erupt all over the body, and the lesions are chock full of spirochetes, making secondary syphilis the most infectious stage. The rashes from secondary syphilis usually resolve within a few weeks to months.
Early latent syphilis occurs within a year of infection, and during that time the spirochetes can re-enter the blood - so this means that during early latent syphilis they can still be found circulating in large numbers in the blood, causing symptoms of secondary syphilis.
However, the late latent phase is generally after a year, and that’s because the spirochetes generally stay within the tiny capillaries of various body organs and tissues.
As it turns out, only a few spirochetes are actually found in the capillaries of tissues and organs, but there is a severe immune response—so severe, that it causes tremendous damage to the cells there. And that triggers the next phase which is tertiary syphilis.
In tertiary syphilis, there’s a type IV hypersensitivity reaction, which means that there’s an immune response that’s mainly led by the T cells and they recruit phagocytes like macrophages, and cause the release of proinflammatory cytokines such as tumor necrosis factor, IL-1, and IL-6.
These include group specific antigen, which are present in all treponemes, species-specific antigen, which are specific to T. pallidum, and cardiolipin, which is a lipid antigen, which interestingly, is present within the spirochetes as well as the cells in our body.