Inflammation of the pachymeninges resulting in localised or diffuse thickening of the dura mater for which no identifiable cause is found. The cranial and/or the spinal dura may be affected. Neurological features include headache, visual disturbance, cranial nerve palsies, ataxia and with spinal involvement, limb weakness, sensory impairment and sphincter disturbances. Diagnosis may be aided by neuroimaging and spinal fluid analysis and dural biopsy.