504 - A case of focal task-specific dystonia of the left lower limb in a 38-year-old woman

Case Diagnosis: Focal task-specific dystonia (FTSD) of the lower limb

Case Description: This is a 38-year-old woman with a history of migraines and ADHD who presented with a 10-year history of difficulty advancing her left limb while walking, prior to which she ambulated without difficulty. Her impairment is worse with walking quickly and absent with running, transfers, or taking stairs. She endorses left-thigh pain but reports that pain has never been her main concern. She previously tried physical therapy focused on strengthening, multiple injections, arthroscopic hip surgery, and open ischiofemoral surgery, all without benefit. Neurologic evaluation and formal gait analysis were non-diagnostic. On physical examination, she walks with left lower-limb extensor posturing but jogs symmetrically. Limb tone is normal. Strength in hip flexion is slightly stronger on the right. Provocative maneuvers of the left hip are negative. Prior EMG/NCS of the left lower extremity was normal. Prior lumbar spine MRI depicted decreased muscle bulk of the left psoas compared to the right.

Discussions: FTSD of the lower limb is a rare condition characterized by abnormal movements or postures with one specific activity, such as walking, running, or cycling. Given the task-dependent posturing without true spasticity seen on examination, we advised the patient that she seemed likely to have FTSD and that her mild pain and weakness were likely secondary to chronically altered gait mechanics. The patient saw a neurorehabilitative physical therapist who, within two visits, facilitated gait improvement during multidirectional stepping and dual-tasking exercises, further supporting the diagnosis.

Conclusions: FTSD of the lower limb is a rare but potentially debilitating condition which can present as gait impairment without other neurologic deficits. It is important to consider the diagnosis in patients presenting with vague difficulty performing specific ambulatory tasks.