The overall mortality of patients with CNS tuberculosis is still significant (approximately 10 percent), infants and the elderly being at greatest risk. Among HIV-infected patients, the mortality from tuberculous meningitis is considerably higher (21 percent in the series of Berenguer et al)—the result of delays in diagnosis and, more importantly, of resistance to antituberculous drugs in some patients (Snider and Roper). Most resistant tuberculosis in developed countries is a result of intermittent, ineffective therapy. Therefore, directly observed therapy for at least 2 months–“short course” (DOTS) has become routine for patients in many areas. (See also “Tuberculous Myelitis” in Chap. 42.) Early diagnosis, as one might expect, enhances the chances of survival. In patients who are treated late in the disease, when coma has supervened, the mortality rate is nearly 50 percent. Between 20 and 30 percent of survivors manifest a variety of residual neurologic sequelae, the most important of which are diminished intellectual function, psychiatric disturbances, recurrent seizures, visual and oculomotor disorders, deafness, and hemiparesis. A detailed account of these has been given by Wasz-Hockert and Donner.
The incidence of neurosyphilis, like that of CNS tuberculosis, declined dramatically in the decades following World War II, with the advent of penicillin. In the United States, for instance, the rate of first admissions to mental hospitals because of neurosyphilis fell from 4.3 per 100,000 population (in 1946) to 0.4 per 100,000 (in 1960). However, in more recent years, the number of reported cases of early syphilis has increased, both in nonimmunocompromised individuals and particularly in HIV-infected ones. Notable also is the shift in clinical presentation of neurosyphilis from parenchymal damage, now quite rare, to one of chronic meningovascular disease, particularly in patients with HIV. Congenital syphilis represents a special problem, which is discussed with developmental diseases in Chap. 37.
Syphilis is caused by Treponema pallidum, a slender, spiral, motile organism. Figure 31-5 summarizes the evolution from the primary infection to the various forms of neurosyphilitic diseases.
The initial event in the neurosyphilitic infection is meningitis, which occurs in approximately 25 percent of all cases of syphilis. The treponeme usually invades the CNS within 3 to 18 months of inoculation with the organism. If the nervous system is not involved by the end of the second year, there is only one chance in 20 that the patient will develop neurosyphilis as a result of the original infection. At the end of 5 years, the likelihood of developing neurosyphilis falls to 1 percent. Usually the meningitis is asymptomatic and can be discovered only by lumbar puncture. Exceptionally, it is more intense and causes cranial-nerve palsies, seizures, stroke, and symptoms of increased intracranial pressure. In the current era, clinicians understandably neglect to consider the possibility of neurosyphilis with these syndromes. The meningitis may persist in an asymptomatic state and, ultimately, after a period of years, may lead to parenchymal damage. In some cases, however, there is a natural subsidence of the meningitis.