Argyll-Robertson Pupil Syndrome
His pupils are small and do not constrict to bright light but constrict with convergence, What is the diagnosis?
Case
You are asked by your Professor to examine the pupils of an interesting 64-year old male patient on the ward. All you are told is that he is demented, deaf, unsteady on his feet with absent tendon reflexes. You find that his pupils are small and do not constrict to bright light but constrict with convergence, i.e. when looking at an object held close to his nose.
What is the syndrome that describes the pupillary response to light? Discuss the neuroanatomy of the syndrome.
Argyll-Robertson Pupil Syndrome
The Argyll-Robertson Pupil Syndrome describes pupils with light-near dissociation: a finding of small, bilateral pupils that do not constrict in response to light, although they do constrict when focusing on near objects. In addition, Argyll-Robertson pupils react less to mydriatics and do not dilate in response to pain.
The pupillary light reflex is composed of afferent (sensory) and efferent (motor) limbs. The afferent pathway carries sensory input through the optic nerve (CN II), and the efferent pathway carries the motor output through the oculomotor nerve (CN III) to the ciliary sphincter muscle of the iris.
The pathophysiology of the Argyll-Robertson Pupil Syndrome is unknown; the most widely accepted theory suggests a lesion at the posterior aspect of the Edinger-Westphal nucleus, where the efferent pupillary fibres travel. The fibres associated with the accommodation reflex are located more anteriorly and are thus unaffected.
What is the most likely diagnosis based on the full clinical presentation?
Neurosyphilis
A finding of Argyll-Robertson Pupil Syndrome is highly suggestive of a diagnosis of neurosyphilis.
Neurosyphilis is the infection of the CNS by the spirochete Treponema Pallidum, which occurs as the spirochete infiltrates the CSF. Early neurosyphilis may be asymptomatic, or present in the form of meningitis, posterior uveitis, or panuveitis. Hearing loss and events of meningovascular thrombosis and ischemia are possible signs of early neurosyphilis as well.
Late (“tertiary”) neurosyphilis is very uncommon in the antibiotic era. When present, tertiary syphilis has two main manifestations:
General Paresis
This presentation usually occurs 10-20 years following primary infection, with its main feature being a gradual onset of dementia. Alongside dementia, the neurological examination may be intact or include dysarthria, hypotonia, tremor, or reflex abnormalities.
Tabes Dorsalis
This presentation of late neurosyphilis is where Argyll-Robertson Pupil Syndrome is most likely to appear. It characteristically manifests as long as decades following primary infection, although earlier presentations have been recorded. Symptoms of tabes dorsalis include sensory ataxia and lancinating, brief pains in the limbs, back, or face. Epigastric pain and bladder dysfunction may be observed. Upon neurological examination, pupillary abnormalities may be found as mentioned, as well as absent lower extremity reflexes and impairment in vibratory and position sensation.
Diagnosis
In the case of clinically suspected neurosyphilis, careful history regarding prior infection must be obtained. If a prior infection is unknown, testing the serum for syphilis is necessary, using nontreponemal (VDRL\RPR) or treponemal tests (FTA-ABS, TPPA, TP-EIA, CIA). In early neurosyphilis, both nontreponemal and treponemal tests are almost always positive. However, in late neurosyphilis, nontreponemal tests may be negative, and thus treponemal tests, which remain positive for life, must be performed.
Once a positive diagnosis of syphilis is established, a lumbar puncture with CSF examination may be necessary. A VDRL test in the CSF is performed, and the results, alongside CSF abnormalities, may give clues regarding the likely manifestation of late neurosyphilis. In general paresis, VDRL is almost always reactive, and elevated lymphocytes and protein are present. In tabes dorsalis, CSF may be normal or show mild lymphocytosis and some protein.
In conclusion, our patient presents several signs suggestive of neurosyphilis. The unique pupil abnormality is the most specific finding, and dementia, hearing loss, ataxia, and lack of tendon reflexes all fit with the diagnosis. Further evaluation for the presence of Treponema Pallidum in the serum and CSF is indicated, and treatment is necessary.
Author
Sapir Dreyer
Year 6 medical student
Hebrew University, Jerusalem
sapirdreyer@gmail.com