The gold standard remains visualization of spirochetes on darkfield microscopy. Those patients afflicted with tabes dorsalis often have pupil irregularities, 50% of which will be the distinctive AR pupil.These patients suffer from sensory ataxia – lack of coordination due to a loss of sensory input into the control of movement (not from cerebellar pathology) and lancinating pains – the sensation of sudden, brief, severe pains over the face, back, limbs that can last from minutes to days.Tabes dorsalis: The posterior columns of the spinal cord and its dorsal root become affected in this stage of syphilis.Other findings to correlate the diagnosis of AR pupil are those suggestive of late-stage syphilis, such as: Additionally, pupils will exhibit slow dilation with atropine (or other mydriatics). Close examination may show an atrophied iris with loss of the radial folds and crypts. The pupils will initially have a sluggish response to light, progressing eventually to a complete absence of the light reflex. Symptoms are usually bilateral and have a gradual onset of months to years. The patient with AR pupil will show small, irregular pupils with light-near dissociation: absent light reflex, prompt constriction with near accommodation. Damage to this area would affect the efferent pupillary fibers located on the dorsal aspect of the Edinger-Westphal nucleus (EWN), which are a part of the light reflex while sparing the fibers associated with the accommodation reflex which lay more ventrally to the EWN. Their research implicates a portion of the rostral midbrain (brainstem) located near the Sylvian aqueduct as the most likely location of the syphilitic lesion. The current leading theory, proposed by Thompson and Kardon (2006) is that syphilis leads to a "dorsal midbrain lesion that interrupts the pupillary light reflex pathway but spares the more ventral pupillary near the reflex pathway." The exact pathophysiology of AR pupils remains unknown. Additionally globally, reports have indicated that syphilis has been on the rise in conjunction with the global HIV/AIDs epidemic. The US CDC data estimates that 5% of MSM with syphilis are also infected with HIV. There is a high rate of co-infection with HIV in those MSM patients who have contracted syphilis. This may be due to the fact that syphilis is more common in MSM, many of whom concurrently also have HIV, or it could reflect two separate groups with increased susceptibility. From 2000 to 2016, the rise in reported syphilis cases is primarily due to increased cases in the men who have sex with men population. The CDC acknowledges, however, that the disease is likely under-reported. According to the CDC: there were 30,676 cases of late and late latent cases of neurosyphilis reported in the United States in 2016. However, in the modern era, the number of cases of primary and secondary syphilis have been increasing every year since 2001, and continue to rise. The exam finding of Argyll Robertson pupils has been rare in the developed world since the advent of penicillin in the 1940s. The exact pathophysiology leading to the AR pupil, however, remains unknown. Neurosyphilis occurs due to an invasion of the cerebrospinal fluid (CSF) by the spirochete which likely occurs soon after the initial acquisition of the disease. Argyll Robertson pupil is found in late-stage syphilis, a disease caused by the spirochete Treponema pallidum.
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