Optic neuropathy secondary to spontaneous intracranial hypotension (SIH) as related to experimental primate model.

We read with great interest the recent article by Yang et al. regarding their primate model investigating optic neuropathy resulting from reduced cerebrospinal fluid pressure. The authors conducted a thorough case-control study looking at the effects of intracranial hypotension from insertion of a lumbar-peritoneal shunt in four rhesus monkeys, adding five control monkeys with lumbar-peritoneal shunt inserted but immediately occluded. This is an innovative study, giving some vital information about the structural damage to the optic nerve that can ensue from decreased intracranial pressures. This study is of particular interest to us given a clinical case we recently encountered. In brief, a 74-year-old man developed slowly progressive vision loss over 9 to 12 months. He had a history of nonpostural headache. On examination, the visual acuities (VA) were 20/125, right eye and 20/20, left eye. The remainder of his examination was significant for a 2þ right relative afferent pupillary defect, right eye dyschromatopsia, and obvious optic atrophy in the right eye with 3þpallor. Visual field testing showed a temporal defect respecting the vertical meridian in the right eye, and superior and inferior constriction in the left eye (Figs. 1A, 1B). Magnetic resonance imaging (MRI) revealed diffuse dural thickening and enhancement in the vicinity of the optic canals bilaterally (Fig. 2A). A lumbar puncture demonstrated an opening pressure of 80 mm H20 and an elevated cerebrospinal fluid (CSF) protein of 88 mg/dL. Cytology was negative. Five days after the lumbar puncture, the patient noted a slowly progressive decline in vision, now also involving the left eye. The visual acuities were 9/200 in the right eye and 20/30 in the left eye. Visual field testing showed worsening (Figs. 1C, 1D). The patient then underwent a lumbar epidural blood patch procedure. Subsequently, the visual loss ceased and the visual fields remained stable in the right eye, and gradually improved in the left eye, over the next 6 months (Figs. 1E, 1F). Repeat neuroimaging demonstrated significantly improved meningeal thickening and decreased enhancement in the region of the optic canals (Fig. 2B). Our presumption is that the visual loss was a consequence of intracranial hypotension, supported by the fact that the progressive loss ceased on the right and function was restored on the left once the blood patch was done. Our MRI of this patient showed dural thickening with noticeable overall morphologic improvement after the patch was placed. This also supports spontaneous intracranial hypotension (SIH) as a probable etiology. Spontaneous intracranial hypotension is an uncommon disorder that is often missed or misdiagnosed due to its variable clinical manifestations, especially in the absence of postural headache. A case series by Horton and Fishman described two patients with visual field loss in the setting of SIH. After blood patch, the perimetry normalized in both subjects. The authors postulated that the visual field defects were likely related to compression or vascular congestion of the intracranial portions of the optic nerve. In SIH, the CSF opening pressure is typically low, but a significant minority of the patients with a documented active CSF leak and typical clinical and imaging manifestations of the FIGURE 1. Visual field at presentation shows a superior and inferior constriction in the left eye (A), and a temporal defect respecting the vertical meridian in the right eye (B). Visual fields worsened in both eyes over the next 2 weeks ([C] left eye, [D] right eye) then after the blood patch gradually improved in the left eye (E) and remained stable in the right eye (F) over the next 6 months.