5) DEGENERATIVE DISEASES - SYPHILIS (TABES DORSALIS)
A Sample Case:A 60 year old female complained of "shooting" pains in the legs and enlargement of the knee joints for about 2 years. Her physician said that she had severe arthritis. The patient began to experience difficulty walking in the dark and urinary incontinence and sought other medical advice.
The neurologic exam demonstrated Argyll Robertson pupils and radiographs of the knees were consistent with arthritic "Charcot type" joints. The patellar and ankle reflexes were absent and there was loss of vibratory and position sense in the lower extremity. The patient's ataxia was evident as she walked with a broad-based gait. She was very nervous when asked to walk or stand with her eyes closed and demonstrated the Romberg sign.
Syphilis is caused by the spirochete Treponema pallidum which may invade the CNS 3 - 18 months after infection. Even when clinical symptoms are referable to only one part of the nervous system post-mortem examination reveals diffuse changes in both the brain and spinal cord. In its most severe form there is progressive mental and physical deterioration. The neurologic symptoms of tabes dorsalis usually develops 15 - 20 years after infection.
Ataxic gait and hyporeflexia are caused by purely sensory deficits due to irritation and destruction of the sensory afferents in the lumbosacral dorsal roots, affecting the incoming heavily myelinated proprioceptive fibers (later seen as demyelination in the posterior white columns). Dorsal root inflammation produces bouts of shooting pains, most common in the legs but they "roam" over the body from the feet to the face. Other paresthesias are described and are associated with impairment of pain, temperature and touch sensation; there is also sensory impairment from the bowel and bladder (S-2,3) accounting for the incontinence.
"Charcot joints" is a neuropathic arthritis, a severe form of osteoarthritis. The arthritic knee joints result from the relative insensitivity of the joints, due to destruction of the dorsal root fibers, and the resultant repeated injury; remaining pain fibers however were still sufficient to permit pain to occur. Charcot joints occur in less than 10 percent of tabes patients.
About 90 percent of the patients exhibit the Argyll Robertson pupils in which the pupils fail to constrict in reaction to light but constrict during convergence when the focus moves from a far to a near object. The cause of this response is unknown but there are usually additional signs of ophthalmoplegia and optic atrophy.