Atypical spontaneous intracranial hypotension (SIH) with nonorthostatic headache

BACKGROUND: Some patients with spontaneous intracranial hypotension (SIH) often do not demonstrate typical orthostatic headache, which is contrary to the typical SIH syndrome. They usually have an obscure and intermittent headache, regardless of their positional change. OBJECT: The objective of this study is to investigate the clinical course of atypical SIH that manifests with diffuse pachymeningeal enhancement, but no orthostatic headaches. METHODS: Between January 1997 and December 2005, we observed a total of 6 patients who revealed atypical presentations including nonpostural headaches and normal cerebrospinal fluid (CSF) pressure, despite the diffuse pachymeningeal enhancement seen on their MR images. For a comparison of the clinical features and the disease course, 13 other SIH patients with typical clinical manifestations were selected as a control group. RESULTS: Cerebrospinal fluid leakage sites were confirmed in only one patient through a variety of diagnostic tools; in contrast, definite focal CSF leakage sites were found in 12 of 13 patients with typical SIH. The 6 atypical SIH patients were treated with conservative treatment, including strict bed rest and intravenous hydration for 2 to 3 weeks. After a mean follow-up of 12 months, their headaches were gradually relieved after 2 to 3 weeks of conservative treatment only. CONCLUSIONS: All SIHs do not necessarily show the typical clinical manifestations. The atypical finding of SIH such as nonorthostatic headache or normal CSF pressure may be the result of a normal physiologic response to the typical SIH as a compensatory reaction. Therefore, when faced with patients showing findings compatible with SIH on the brain MR images, regardless of nonpostural headache, atypical SIH should be suspected.