1423 - Atypical Arachnoiditis

Case Diagnosis: Arachnoiditis

Case Description: 71F with an eight-month history of foot drop and episodic sharp, burning right buttock pain radiating down the posterior leg and heel. Her exam revealed intact BLE sensation and motor strength, except for worsening right ankle weakness with dorsiflexion and plantarflexion, with absent Achilles reflex. Over time, she developed sensation deficits in the right L5 and S1 dermatomes, as well as the left S1 dermatome. Her CT showed instrumentation from T2-S1 with spinal fusion and anterior discectomy at L4-L5 and L5-S1. MRI demonstrated no spinal canal or foramina narrowing, with an empty appearance to the thecal sac along the length of the lumbar spine, and nerve roots adherent to the inner margin of the thecal sac; compatible with arachnoiditis. She was treated conservatively with Tramadol, Pregabalin, Ropinorole, Gabapentin, physical therapy, and osteopathic manipulative treatment for pain, a custom AFO for ankle stability, and has been followed for 3 years.

Discussions: Arachnoiditis is the persistent inflammation of the meningeal arachnoid layer and subarachnoid space. Less than 1000 cases have been reported in literature, and spinal surgery is currently the most common risk factor. This case demonstrates the unpredictable onset and variable symptom presentation of adhesive arachnoiditis following an etiological event, such as spinal surgery. High clinical suspicion in the setting of leg pain, sensory changes, and weakness, and the use of MRI was crucial for diagnosis. With no known cure, arachnoiditis requires a multimodal approach to management, such as surgical or supportive therapies, to improve quality of life.

Conclusions: This case illustrates an atypical presentation of adhesive arachnoiditis, manifesting as postoperative foot drop following scoliosis fusion surgery. Without pain as a dominant symptom and delayed radiographic confirmation, this challenges the conventional clinical picture. Recognizing radiculopathy with delayed motor deficits as arachnoiditis may aid earlier interventions and improve neurological outcomes.