Working Diagnosis:
Focal task-specific dystonia or paroxysmal kinesiogenic dystonia associated with Parkinsonism

Treatment:
Initially referred to Sports Medicine clinic for evaluation of foot pain and posturing. He underwent medical bike fit with PT with no improvement of symptoms. Care was transferred to Neuromuscular/Movement Disorder clinic. He has tried oral anti-spasmodic medications, Baclofen 10-20mg prior to bike rides then Clonazepam 1mg TID, with no effect. Then started on Trihexyphenidyl 2mg BID for tremor and dystonia suppression, with modest effect. Botox injections (100 units) performed to the tibialis posterior and flexor digitorum longus muscles with no effect. Started on Synthroid per primary care doctor.

Outcome:
Discussed with patient that he may continue to bike as tolerated; however, pain level and perceived ankle instability may necessitate reduction in bike riding distance at least temporarily. Return to biking at the intensity prior to injury will be determined by his response to oral tremor/tone suppressing medications and Botox injections. Overall, he is doing ok and stable. He does continue to have left foot dystonia and tremors that are present at rest. He has since been diagnosed with Parkinson's disease and is starting Carbidopa/levodopa.

Author's Comments:
Focal task-specific dystonias most often affect the upper limb and are characterized by involuntary sustained muscle contraction. They are often associated with activities such as writing, playing an instrument, or playing sports. In this case, the patient experienced a dystonic posturing of his right foot with prolonged biking, which has not been reported in the literature to date. Symptoms were elicited and captured on video with prolonged stationary biking. Dystonias are often associated with a central movement disorder, such as Parkinson's disease, therefore an extensive work-up is warranted in this case, especially given history of essential tremor.

Editor's Comments:
Focal task specific dystonia, (FTSD)typically begins in adulthood with symptom onset in the third to sixth decade. FTSD is more common in men, and it usually affects the arm, facial muscles or larynx.
FTSD typically presents as an insidious, painless loss of dexterity caused by performance of a specific, often over-practiced task. Symptoms progress over time to trigger uncontrolled activation of muscle groups, leading to abnormal postures and movements. Early in the disease course, the dystonia typically is triggered only by the performance of a specific task, but over time spreads to involve other tasks, or even spreads to previously unaffected areas of the body.
Current treatment modalities for FTSD include oral medication, chemodenervation, surgery and physical therapy. Anticholinergic agents like trihexyphenidyl, as well as other medications, such as primidone, baclofen, and phenytoin have been tried with inconsistent responses and frequent intolerable side effects. Chemodenervation with botulinum neurotoxin (BoNT) type A has been the mainstay of treatment for FTSD (2)

References:
1.Cifu D, Eapen B (2021). Braddoms Physical Medicine and Rehabilitation.

2.Stahl CM, Frucht SJ. Focal task specific dystonia: a review and update. J Neurol. 2017 Jul;264(7):1536-1541. doi: 10.1007/s00415-016-8373-z.

3.Murgai AA, Jog M. Focal limb dystonia and tremor: Clinical update. Toxicon. 2020 Mar;176:10-14. doi: 10.1016/j.toxicon.2020.01.004.

4.Wu LJ, Jankovic J. Runners dystonia. J Neurol Sci. 2006 Dec 21;251(1-2):73-6. doi: 10.1016/j.jns.2006.09.003. Epub 2006 Nov 9. PMID: 17097111.

5.Cutsforth-Gregory, Jeremy K, Ahlskog, J. Eric, McKeon, Andrew, Burnett, Melinda S, Matsumoto, Joseph Y, Hassan, Anhar, Bower, James H. (2016). Repetitive exercise dystonia: A difficult to treat hazard of runner and non-runner athletes. Parkinsonism Related Disorders, 27, 74-80.

Return To The Case Studies List.