Idiopathic intracranial hypertension (IIH) is a disorder of unknown etiology, which is characterized by increased intracranial pressure (ICP). Other names have included benign intracranial hypertension and pseudotumor cerebri. The syndrome of IIH is characterized by clinical signs and symptoms of increased ICP but no evidence of intracranial mass, infection, hydrocephalus, or other apparent structural central nervous system pathology on neuroimaging studies and cerebrospinal fluid (CSF) examination.
It is most common in obese women of childbearing age, and is more common in hypertensives and during pregnancy. The annual incidence has been estimated to be 3/100,000.
Other causes of generalized intracranial hypertension that are not idiopathic include venous sinus thrombosis, endocrinopathies, hyper/hypovitaminosis A, anemia, recent use of certain medications (tetracycline, indomethacin, nalidixic acid, nitrofurantoin, oral contraceptives, lithium), and prolonged use of corticosteroids. Other systemic conditions that mimic aspects of IIH include sleep apnea, pre-eclampsia, chronic obstructive pulmonary disease, right-sided heart failure, uremia, renal failure, systemic lupus erythematosus (SLE), coagulation disorders and hyperthyroidism.
Many neurologic symptoms are blamed on antecedent immunizations, but it is difficult to evaluate true causality. A common concern is when patients hear about small studies suggesting causal relationships between a vaccination and a particular disease. Studies and vaccine modification (such as the acellular pertussis vaccine) are ongoing to minimize risk to patients.
Vaccines against the following diseases and infections are currently available:
I.Anthrax: Recent studies among immunized military personnel have shown no increase in disability among those receiving the vaccine.
II.Japanese encephalitis: Acute disseminated encephalomyelitis (ADEM) has been reported to occur after vaccination. Actual incidence is unclear, as several studies show wildly different rates, ranging from 0 cases in 813,000 vaccinations to 1 in 600. Two studies showed incidence rates between 0.2 and 2 in 100,000.
III.Haemophilus influenzae type B: no complications have been reported.
IV.Hepatitis B: There has been public concern about increased risk of MS, but this was disproved in a large study.
V.Influenza: There may an increased frequency of Guillain-Barré syndrome (GBS) following influenza vaccination. Incidence of giant cell arteritis may also be increased.
VI.Measles: This vaccine is ordinarily combined with mumps and rubella (MMR) vaccines. Except for febrile seizures in children who are genetically predisposed, neurologic complications are uncommon but controversial. There are case reports of ADEM after measles vaccine, but that risk is very minor compared to the substantially higher risk of ADEM and subacute sclerosing panencephalitis from natural measles. In a very large study, MMR vaccine was shown to have no increase in risk of neurologic complications. A 1998 paper by Wakefield that gave rise to the belief that the MMR vaccine might be associated with increased rates of autism has been discredited and has been retracted by the Lancet.
VII.Meningococcus: There was concern for increased incidence of GBS after receiving the Menactra formulation, but two large safety trials were unable to reproduce this risk.
VIII.Pertussis: The new, acellular pertussis vaccine (diphtheria and tetanus toxoids and pertussis—DTaP) has replaced the diphtheria, tetanus toxoid, and pertussis (DTP) vaccine after many concerns about increased neurologic complications. These complications appear to be much less frequent with the new vaccine. Simple febrile seizures, with no long-term effects, can occur within 24 hours of administration. Autism, epilepsy, and hypotonic/hyporesponsive episodes, all previously related to the DTP vaccine, are much less common now.
IX.Pneumococcus conjugate: There is a small increase in the frequency of seizures, usually febrile, in children.
X.Poliomyelitis: Paralytic poliomyelitis is the only known complication of oral polio vaccine (OPV). It is especially a concern for immunodeficient contacts. The inactivated polio vaccine (IPV) is now replacing it in most countries to reduce this risk.
XI.Rabies: Whole-virus vaccines that contain myelin basic protein are associated with ADEM and polyneuritis within 2 weeks after immunization.
XII.Rubella: Transient arthralgias may develop in up to 40% of patients. No causal evidence exists for association with polyneuritis or other neuropathies.
XIII.Toxoids: These vaccines contain antigens from toxins, not from the microbes themselves. Tetanus and diphtheria are the most common and are often given together. Allergic hypersensitivity is the most common (though rare) complication. Demyelinating neuropathy with complete recovery has also been reported.
XIV.Smallpox: Severe, usually transient headaches are common after vaccination.
XV.Varicella: There have not been any serious neurologic complications. The theoretic concern of a shift to more serious adult zoster infections as childhood immunization wanes will be tested in the years to come.
XVI.Human papilloma virus: most common events include headache, nausea, dizziness, and syncope. Rare case reports implicate GBS and ADEM.
XVII.Other agents: Chemical vehicles, preservatives, and contamination have caused complications. Aluminum, commonly in diphtheria, tetanus, and hepatitis A and B vaccines, rarely causes a myofascitis. Mercury was used until 1999 in several preparations. Bovine products carry the risk of prion diseases but have been well monitored in the United States.
Normal values of intracranial pressure (ICP) range from 5 to 15 mm Hg (torr), which equals 65 to 200 mm cerebrospinal fluid (CSF) or H2O (conversion: 1 torr = 13.6 mm H2O). Factors that determine the level of ICP are the volume of intracranial contents and arterial and venous pressures. After the cranial sutures fuse, the skull becomes an inelastic, closed container with a fixed total intracranial volume consisting of 3 components: brain, CSF, and blood. The Monroe-Kellie doctrine states that the sum of intracranial brain tissue, CSF, and blood volumes is constant; therefore, an increase in the volume of one must be compensated by an equal decrease in another compartment. Slow increases in the volume of one compartment can be compensated by decreases in the others, but a rapid rise in ICP is not well tolerated and increases the risk of herniation or the occurrence of global ischemia and is a neurologic emergency. Cerebral perfusion pressure (CPP) is critical to maintain adequate cerebral blood flow (CBF) and is calculated as a difference between mean arterial pressure (MAP) and ICP (CPP = MAP-ICP). CPP less than 50 mm Hg is detrimental to brain function and survival. Following any major cerebral injury, ICP should be maintained as close to normal as possible, to provide a margin of safety. Continuous ICP monitoring provides useful information about “pressure waves” and may be used to guide treatment. Plateau waves, consisting of episodic surges in ICP (sometimes exceeding 450 mm H2O) can occur several times an hour, especially with pain and iatrogenic maneuvers, such as suctioning, and are associated with increased risk of herniation.
Clinical presentation of increased ICP depends on the underlying process, compartmentalized or diffuse, and whether it is acute or chronic. Manifestations of headache, papilledema, diplopia, or focal signs may occur. Cushing’s triad of bradycardia, hypertension, and slowing of respiration may occur in patients with significant increased ICP and as such these patients will additionally have a depressed level of consciousness. If there is an element of brainstem compression or involvement of the right insula, patients may develop cardiac arrhythmias, such as atrial fibrillation, nodal and ventricular bradycardia, large T waves, prolonged QT intervals, and changes in ST segments.
Space-occupying lesions, cerebral edema (cytotoxic edema secondary to brain infarction or vasogenic edema commonly caused by tumor), trauma, intra/extra-axial hemorrhages (hemorrhagic stroke, subarachnoid hemorrhage, subdural hematoma, epidural hematoma), infections, venous sinus thrombosis, and pseudotumor cerebri may increase ICP. An acute rise in blood pressure beyond the autoregulatory curve causes an elevated ICP, as seen in hypertensive encephalopathy; chronic hypertension does not cause a change in ICP. Processes that increase venous pressures cause increases in ICP and include jugular compression (as reflected by Queckenstedt’s test during LP), superior vena cava obstruction, congestive heart failure (CHF), or Valsalva maneuvers. Postural effects alter the pressures in the intracranial venous sinuses, which in turn alter the CSF pressure.
Decreased ICP may occur in the setting of CSF leakage, either spontaneously through openings in the dura to sinuses or mastoid, after lumbar puncture or neurosurgery, or through overshunting. Postural headache, similar to that observed after lumbar puncture, is a frequent symptom. Diagnosis is confirmed by demonstration of CSF leak on cisternogram or other evidence of CSF leak (positive glucose test in pharyngeal secretions). MRI may show meningeal enhancement. Spontaneous remission may occur, and treatment depends on the cause; occasionally dural graft may be necessary.
