Abducens nerve paresis in spontaneous intracranial hypotension syndrome.
2005-03-30

Editor, Over the past decade the rare syndrome of spontaneous intracranial hypotension (SIH) has been recognized with increasing frequency. Most SIH patients are found to have spontaneous cerebrospinal fluid (CSF) leaks and have unique, clinically distinct imaging findings, which confirm the diagnosis (Lay 2002). Spontaneous intracranial hypotension is a benign and usually self-limiting syndrome of orthostatic headache in association with one or more of numerous symptoms, including nausea, vomiting, horizontal diplopia, unsteadiness or vertigo, altered hearing, neck pain or stiffness, interscapular pain and, occasionally, transient visual obscurations, blurred vision, visual field defects, photophobia and nystagmus (Mokri 2001; Lay 2002). The headache is relieved when the patient spends a few minutes in a supine position and becomes worse in an upright position. By definition, the opening CSF pressure is low; however, the pressure may be normal (Mokri 2001, 2003; Lay 2002). Spontaneous intracranial hypotension is more common in women than men (Diaz 2001). Stigmata of connective tissue abnormalities, especially abnormalities of fibrillin and elastin, are seen in a notable minority of patients, pointing to weakness of the dural sac as one of the aetiological factors (Mokri 2001, 2003; Schievink et al. 2004). The locations of the leaks are mainly cervical or at the cervicothoracal junction (Thoemke et al. 1999; Mokri 2001). Brain and spinal magnetic resonance imaging (MRI) studies show diffuse pachymeningeal gadolinium enhancement, frequently in association with sinking of the brain, and less frequently with subdural fluid collections, engorged cerebral venous sinuses, enlarged pituitary gland, or decreased size of the ventricles (Thoemke et al. 1999; Diaz 2001; Mokri 2001, 2003; Lay 2002). Although conservative measures are often undertaken first, epidural blood patch (EBP − injection of autologous blood in the epidural space) is the treatment of choice. For those who fail EBP, surgery may need to be undertaken in those cases with clearly identified leaks (Mokri 2001; Lay 2002). A 39-year-old woman had severe orthostatic headache, nausea, vertigo and tinnitus over a period of several weeks in November and December 2003. Lumbar puncture revealed a low− normal CSF pressure. Over the next weeks she noted neck stiffness and horizontal diplopia. On examination in January 2004, visual acuity was 20/20 in each eye with correction. No visual field defect was detected. There was a right abducens nerve paresis resulting in 7 degrees of esotropia in primary gaze. An MRI scan demonstrated diffuse pachymeningeal gadolinium enhancement and small bilateral subdural effusions (Fig. 1). The clinical history, ocular findings, and MRI features were so characteristic of SIH that a second lumbar puncture was deemed unnecessary. The patient was treated by EBP. Her headache and the right abducens nerve paresis resolved over the next 4 weeks. The MRI scan of a 39-year-old woman with SIH demonstrated diffuse pachymeningeal gadolinium enhancement and small bilateral subdural effusions. Spontaneous intracranial hypotension is a rare syndrome, characterized by orthostatic headaches, characteristic aspects on MRI, and, usually, low CSF pressure. It is thought that in SIH the brain sags and exerts pressure and traction on meningeal and vascular structures, causing headache, a stiff neck and nausea (Horton & Fishman 1994; Christoforidis et al. 1998). Vertigo and tinnitus probably result from changes in intralabyrinthine pressure (Christoforidis et al. 1998). Visual symptoms were reported in 17 of 40 patients (42.5%) with SIH. They included diplopia and occasionally transient visual obscurations, blurred vision, visual field defects, photophobia and nystagmus (Horton & Fishman 1994; Christoforidis et al. 1998; Mokri 2001; Lay 2002). Diplopia occurred in 30% of patients. Inferior displacement of the brain stem is thought to stretch the abducens nerve, which is anchored to Grubber's ligament, thus causing diplopia. Crowding of the optic nerves in the chiasmatic cistern is thought to cause the visual field defects (Horton & Fishman 1994; Christoforidis et al. 1998). Epidural blood patch is the treatment of choice (Mokri 2001; Lay 2002). In our patient all findings resolved after treatment.