A case of idiopathic hypertrophic cranial pachymeningitis manifested only by positive rheumatoid factor and abnormal findings of the anterior falx.

In this report, we present a rare case of a 52-year-old man with a unique form of hypertrophic pachymeningitis involving the anterior part of the falx and who was positive for rheumatoid factor. The clinical symptom was only headache, without any cranial nerve palsies or ataxia. Diagnosis was made by gallium scintigraphy and magnet resonance imaging but was not confirmed by dural biopsy. Treatment with corticosteroid alone was extremely effective for him, while in most cases hypertrophic pachymeningitis recurs or progresses despite the treatment.