and choroid, and optic nerve) and cause local inflammation and edema. In primary or secondary syphilis, invasion of the meninges may result in lymphocytic and plasma cell infiltration of perivascular spaces (Virchow-Robin spaces). The extension of cellular immune response to the brainstem and spinal cord causes inflammation and necrosis of small meningeal vessels. In tertiary syphilis, reactivation of chronic latent infection may result in meningovascular syphilis, arising from endarteritis obliterans of small, medium, or large arteries supplying the CNS. The parenchymal syphilis, presents as tabes dorsalis and general paresis. Tabes dorsalis thought to be due to irreversible degeneration of nerve fibers in posterior columns of the spinal cord involving the lumbosacral and lower thoracic levels. The general paresis is caused by meningeal vascular inflammation and ependymal granulomatous infiltration may lead to neuronal loss, along with astrocytic and microglial proliferation and damage may preferentially occur in the cerebral cortex, striatum, hypothalamus, and meninges. Concurrent infection of T. pallidum with human immunodeficiency virus (HIV) has been found to affect the course of syphilis. Syphilis can lie dormant for 10 to 20 years before progressing to neurosyphilis, but HIV may accelerate the rate of the progress. Also, infection with HIV has been found to cause penicillin therapy to fail more often. Therefore, neurosyphilis has once again been prevalent in societies with high HIV rates and limited access to penicillin. Diagnosis To diagnose neurosyphilis, cerebrospinal fluid (CSF) analysis is required. Lumbar puncture ("spinal tap") is used to acquire CSF. The Venereal Disease Research Laboratory test of the CSF is the preferred test for making a diagnosis of neurosyphilis. A positive test confirms neurosyphilis but a negative result does not rule out neurosyphilis. Due to the low sensitivity of the CSF VDRL, fluorescent treponemal antibody absorption test (FTA-ABS) can be used to supplement VDRL. Reported sensitivity is variable. False-negative antibody test result occurring when antibody concentration is so high that agglutination reaction cannot occur, which is typically seen during secondary stage and can be overcome by diluting test sample 1:10. CSF white blood cell count is often elevated in the early stages of neurosyphilis, ranging from about 50 to 100 white blood cells/mcL with a lymphocyte predominance. Cell counts are typically lower in late syphilis. Regardless of syphilis disease stage, the absence of CSF white blood cells rules out neurosyphilis. Treatment Penicillin is used to treat neurosyphilis. Two examples of penicillin therapies include: Aqueous penicillin