Idiopathic Hypertrophic Spinal Pachymeningitis with Spinal Cord Lesion: A Case Report

Idiopathic hypertrophic spinal pachymeningitis (IHSP) is a rare, diffuse inflammatory fibrosis of the dura mater that can lead to spinal cord compression. Though the optimal treatment is controversial, some reports recommend decompressive surgery and postoperative steroid therapy. However, we encountered a case of pachymeningitis that worsened after decompressive surgery. A 79-year-old woman presented with gait disturbance and bilateral lower extremity weakness that began 6 months prior. She had radiating pain on the C5 and T1 dermatomes and clumsiness in both hands. Magnetic resonance imaging (MRI) revealed diffuse thickening of the posterior longitudinal ligament of C6 to T4/5 and ligamentum flavum of C3/4 to T4/5, causing central canal stenosis and compressive myelopathy. She underwent posterior decompressive laminectomy from C4 to T1 total (T2 subtotal) and cervicothoracic screw fixation. During surgery, we found severe adhesion of the posterior longitudinal ligament and ligamentum flavum to the dura mater. Chronic inflammation with fibrosis and lymphoplasmacytic infiltration were present. After surgery, the patient's motor weakness worsened. Despite steroid treatment, her symptom severity fluctuated. Follow-up MRI obtained 3 months postoperation revealed high signal intensity from C5 to T2, possibly indicating aggravated compressive myelopathy. Thus, in this case, decompressive surgery and steroid therapy were detrimental.