Neurosyphilis

In the AIDS population up to 1-3% of patients are positive to cerebrospinal fluid (CSF) Veneral Disease Research Laboratory (VDRL) tests. Without therapy, 5-10% of patients develop clinical evidence of neurosyphilis.

The CNS manifestations of syphilis can be broadly classified into meningeal and parenchymal. Meningeal manifestations range from the acute and more subtle and chronic forms of meningitis and meningoencephalitis up to the formation of circumscribed masses. These gummas are composed, similarly to those in all other sites in the body, of granulation tissue surrounded by mononuclear epithelial and fibroblastic cells and, intracranially, usually located over the cerebral convexities, adherent to both dura and brain parenchyma.

Parenchymal manifestations include two types of vasculitis, respectively Heubner's and Nissl's endarteritis, the former affecting large and medium-sized arteries with resultant irregular luminal narrowing and ectasia, the latter primarily involving small vessels in which a luminal narrowing occurs as a consequence of intense proliferation of endothelial and adventitial cells. Vascular neurosyphilis may present with focal neurological deficits as a consequence of arterial occlusion. For so-called meningovascular syphilis the usual interval of infection to symptom onset in the general population is 5 to 10 years.

In the later stages of neurosyphilis two neurological clinical pictures, general paresis and tabes dorsalis, are classically described.

General paresis correspond clinically to a spectrum of disturbances involving cognitive functions and including hallucinations, illusions, delusions, alterations of personality, memory loss and speech difficulties, and associated with a general hypereflexivity and with the Argyll Robertson pupil. General paresis appears to be the result of diffuse parenchymal damage associated with chronic meningoencephalitis.

Tabes dorsalis corresponds clinically to a triad of symptoms (lightning pains, dysuria, and ataxia) and a triad of signs (Argyll Robertson pupil, areflexia, and loss of proprioception) and is the reflexion of a myelopathy characterized by atrophic, degenerated, and demyelinated dorsal nerve roots and posterior spinal columns.

The classically described time intervals from infection to symptom onset of 20 and 25-30 years for, respectively, general paresis and tabes dorsalis appear to be shortened in HIV-infected patients.

Meningovascular syphilis responds promptly to treatment with penicillin G. Treatment of general paresis and tabes dorsalis is far less successful.

Diagnostic confirmation of neurosyphilis is based on laboratory exams. CSF and serum VDRL tests are highly specific for active neurosyphilis but the tests are negative in approximately one half and from one third to one half of patients respectively. Serum fluorescent treponemal antibody absorption test (FTA), is more sensitive. In cases of negative CSF VDRL presumptive diagnosis of neurosyphilis is based on CSF pleocytosis and elevated CSF protein levels, associated with positive serum FTA.

Imaging findings include meningeal enhancement and small infarcts or foci of ischaemia with a predilection for the basal ganglia and the middle cerebral artery regions, revealed in the subacute phase by areas of contrast enhancement. Cerebral atrophy is a frequent acompaniment. Gummas are visible as mass lesions, with nodular or ring enhancement, at the brain surface. MR is superior to CT scan in identifying in particular small lesions corresponding to foci of ischaemia.

FS