Focal idiopathic hypertrophic pachymeningoencephalitis.

Cranial pachymeningitis is typically a diffuse granulomatous disease that involves the dura mater extensively without intra-axial involvement. We report a rare case of focal idiopathic hypertrophic pachymeningoencephalitis (IHP) focally affecting the right parietal dura mater and adjacent parietal lobule. A 43-year-old male suffered from acute onset of rhythmic twitching over the left abdominal muscles that had persisted for more than 4 hours. Neurologic examination revealed mild weakness and impaired sensation in the left lower limb. Electroencephalography disclosed active focal spikes in the right parietal region and brain magnetic resonance imaging showed a well-enhanced lesion involving the right parietal lobe and its overlying dura mater. Surgical removal of the lesion revealed infiltration by abundant chronic inflammatory cells without granuloma formation, caseous necrosis or vasculitis. After surgery, the patient was treated with steroid, which was tapered off 5 months later. Serial magnetic resonance imaging follow-up revealed that the parenchymal mass and perifocal edema had completely disappeared 6 months after the operation. We suggest that early recognition of this rare IHP, together with proper surgical intervention and concomitant steroid therapy, may be beneficial for long-term remission.