Cerebral coenuriasis (coenurus cerebralis) is an uncommon infestation by larvae of the tapeworm Taenia multiceps. It occurs mainly in sheep-raising areas where there are many dogs, the latter being the definitive hosts. The larvae form grape-like cysts, most often in the posterior fossa, which obstruct the spinal fluid pathways and cause signs of increased intracranial pressure. Surgical removal is possible.
Another cestode, Spirometra mansoni, may migrate within the brain, leaving a visible track as it moves. Subcutaneous nodules are the most common lesions. This parasite is found predominantly in the Far East.
The nervous system may also be invaded directly by certain worms (Ascaris, filaria) and flukes (Schistosoma, Paragonimus). These diseases are virtually nonexistent in the United States except among those who have recently returned from endemic areas. Schistosomiasis, however, is of such great importance and often invades the nervous system in such characteristic ways that it is considered below in detail.
The ova of trematodes seldom involve the nervous system, but when they do, the infecting organism is usually Schistosoma japonicum and, less often, Schistosoma haematobium or Schistosoma mansoni. It is said that S. japonicum has a tendency to localize in the cerebral hemispheres and S. mansoni in the spinal cord, but there have been many exceptions. The cerebral lesions form in relation to direct parasitic deposition of eggs in blood vessels and take the form of mixed necrotizing and ischemic parenchymal foci that are infiltrated by eosinophils and giant cells (Fig. 31-8) (Scrimgeour and Gajdusek). The lesions do not calcify.
Schistosomiasis is widespread in tropical regions; 80 percent of cases are in sub-Saharan Africa. North American neurologists have little contact with it except in travelers who have bathed in lakes or rivers where the snail hosts of the parasite are plentiful. The initial manifestation may be a local skin irritation at the site of entry of the parasite (swimmer’s itch), or a large serpiginous urticarial rash on the trunk, Katayama fever, particularly likely to occur in prior exposure, but the patient frequently does not offer this information unless sought. A small proportion of patients develop neurologic symptoms several months after exposure. Headaches, convulsions (either focal or generalized), and other cerebral signs appear; with lesions of larger size, papilledema may develop, simulating a brain tumor. It has been hypothesized that travelers are more prone to develop symptomatic nervous system disease because of an intense inflammatory reaction surrounding the deposited eggs.
Some types of Schistosoma infections (also called Bilharzia), mainly mansoni, tend to localize in the spinal cord, causing an acute or subacute myelitis that is concentrated in the conus medullaris. The clinical picture is of a subacutely developing transverse cord lesion. There is often preceding leg or radicular pain and bladder control is affected prominently. We have observed a few cases in students returning from Africa; their lesions were in the conus. Unless treated immediately, there may be permanent paralysis of the legs and bladder from inflammatory and microvascular destruction of the lower cord.
Eosinophilia is common in symptomatic individuals and there is a serologic test but it often becomes negative soon after the initial infection. Examination of the CSF in the myelitic form discloses a pleocytosis, sometimes with an increase in eosinophils (more than half of patients), increased protein content, and increased pressure. Diagnosis is made by the finding of eggs in stool or urine. Serology is probably more sensitive. The other major trematode, Paragonimus, has been known to invade the brain in up to one-quarter of cases, where it creates a solitary granulomatous nodule comparable to that seen in schistosomiasis.