Proposed mechanisms for IIH include decreased cerebral venous outflow secondary to venous stenoses (structural abnormalities) or cerebral venous thrombosis; venous hypertension; increased CSF outflow resistance at the level of the arachnoid granulations or CSF lymphatic drainage sites; increased abdominal, pleural, and cardiac filling; central venous pressures with secondary increase in intracranial venous pressure due to obesity; altered sodium and water retention mechanisms; carbon dioxide retention for instance due to sleep apnea; and abnormalities of vitamin A metabolism.
The diagnosis of IIH is based on detailed history, clinical examination, laboratory tests, brain imaging, lumbar puncture and CSF pressure measurements. Modified Dandy criteria used for the diagnosis of PTC are:
Symptoms and signs of raised intracranial pressure (ie, headache, diplopia, transient visual loss, pulsatile tinnitus, papilledema, permanent visual loss)
No other neurologic abnormalities or impaired level of consciousness
Raised CSF pressure with normal CSF composition
No etiology for intracranial hypertension on neuroimaging
No other apparent cause of intracranial hypertension
History typically includes headache, diplopia, tinnitus, and transient/complete visual loss. Eye examination findings include positive relative afferent pupillary defect (RAPD) in some patients, diplopia, loss of visual field (typically in the inferotemporal region), decreased visual acuity, and dysfunction of color vision. Funduscopic examination reveals unilateral or often bilateral symmetric or asymmetric optic disc edema, macular edema, or exudates, choroidal folds, and retinal neovascularization. Examination of cranial nerves may show deficit (listed in decreasing frequency) of abducens, occulomotor, trochlear, olfactory, trigeminal, or facial and auditory nerves.
Laboratory tests are performed to assess for other causes of optic nerve head edema and may include CBC, serum electrolytes, erythrocyte sedimentation rate, ACE level, serum iron, total iron binding capacity, autoimmune profile, and coagulation profile. Brain imaging must be obtained in patients with headache and papilledema to rule out any space-occupying lesion or other secondary causes of raised intracranial pressure. Neuroimaging includes CT scan brain and MRI brain with MRV. MRI brain with contrast and MRV are the imaging modalities of first choice. CT scan of the brain is done in cases where MRI brain is contraindicated, such as in patients with pacemakers, metallic stents, clips, or foreign bodies.
Patients with IIH have normal-appearing brain parenchyma and ventricles on CT scanning and MRI; the abnormalities that can be seen on MRI include posterior sclera flattening (43%-80%), distended perioptic subarachnoid space (45%-67%), postcontrast enhancement of the prelaminar optic nerve (7%-50%), empty sella (25%-80%), intraocular protrusion of the prelaminar optic nerve (3%-30%), vertical tortuosity of the orbital optic nerve (40%), tonsillar ectopia, narrowing of the Meckel cave and cavernous sinuses, meningoceles, widening of the foramen ovale, and slitlike ventricles. MRV is performed to assess for cerebral sinus venous thrombosis; otherwise, in IIH, it may show narrowing of the transverse sinus but is not specific for IIH.
Lumbar puncture for CSF opening pressure measurement and CSF routine examination is an important diagnostic test. CSF pressure of < 200 mm H2O is normal, 200-250 mm H2O is equivocal, and > 250 mm H2O is high. Lumbar puncture is done in lateral decubitus position because the prone or sitting position can give false high readings, as do anxiety and pain. Repeated lumbar puncture attempts, hyperventilation, and CSF pressure-lowering drugs can give false low readings. CSF is tested for cell count, proteins, glucose, culture, and sensitivity, and to assess for other causes of papilledema—for instance, with venereal disease research laboratory (VDRL) testing, mycobacterium testing, cryptococcal antigen testing, Lyme disease testing, and cytology. CSF cell count, protein levels, and glucose levels are normal in PTC.
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Cite this: Sumaira Nabi, Muhammad Fateen Rashid, Shahzad Ahmed. Neurology Case Challenge: A 19-Year-Old With Tinnitus, Vision Problems, and Headaches - Medscape - May 31, 2022.