Idiopathic Spinal Arachnoiditis Presenting With Acute Bilateral Lower Extremity Weakness

Abstract

Arachnoiditis is a rare inflammatory disorder of the arachnoid membrane that may result in progressive neurological deficits. Due to its nonspecific clinical presentation and variable radiological findings, diagnosis remains challenging. A 61-year-old female presented with a 1-week history of progressive numbness and weakness in the bilateral distal lower extremities, resulting in inability to ambulate. Neurological examination revealed bilateral hypoesthesia below the L1 level and severe motor weakness. Lumbar magnetic resonance imaging demonstrated a diffuse intradural hypointense appearance on T2-weighted images extending from the conus medullaris to the L4–L5 level without contrast enhancement. Surgical exploration was performed for diagnostic and therapeutic purposes. No intradural mass lesion was identified; however, marked nerve root edema and extensive arachnoid adhesions were observed. Adhesiolysis and duraplasty were performed. Postoperatively, the patient showed significant neurological improvement. Idiopathic arachnoiditis should be considered in the differential diagnosis of acute or subacute bilateral lower extremity weakness. Surgical intervention may be beneficial in selected patients for both diagnosis and symptom relief, even when radiological findings persist.