Objective: To report a case of peripheral myoclonus of the lower extremity after injury.

Background: Peripheral myoclonus arises as a consequence of a peripheral nervous system lesion producing hyperactive motor discharges to its muscle (e.g. hemifacial spasm). Trauma is a possible cause of movement disorders. However, this etiology remains a controversial issue as cause and effect relationships have in many cases been difficult to establish. It is well established that brain trauma can cause movement disorders. However, the idea that peripheral trauma can trigger abnormal movements has rarely been reported.

Methods: Literature review spanning 1967-2018 was conducted via Pubmed. Search terms were “Peripheral myoclonus”, “myoclonus”, and “myoclonus and nerve injury”. Only English language publications were evaluated.

Results: A 50 year old male with a past medical history of mild developmental delay presented with a 2 year history of right lower extremity involuntary movements. He reports a recent fall on to his knees. Denies any fractures or physical injury to the leg. After 1 month he noticed constant twitching of the right hamstrings. This occurs only when standing and disappears when sitting, laying down, or walking. On exam, he has non-rhythmic large amplitude myoclonic jerks in the right medial hamstring and extends to the right adductors. There was tightening of muscles on that side. Movements disappear when patient starts walking. These movements were not associated with voluntary movements or reflex stimuli, and there was no evidence of weakness, impairment of vibration, pinprick of touch sense, or cerebellar or cranial nerve dysfunction. An MRI L-spine was obtained and showed a mild herniated disc at L4-L5 but no other abnormalities. The patient was treated with Botox injections with significant improvement of symptoms.

Conclusions: Historically, use of the term “myoclonus” has been restricted to phenomena of central origin. Peripheral myoclonus of the extremities following injury is extremely rare. It has been reported in a patient with Schwann cell sarcoma of the crural nerve, in a case of bracial plexus injury, after traumatic fracture of the humerus, a patient who experienced myoclonus of the 4th dorsal interosseous muscle several days after trauma to the elbow, and myoclonus of an arm stump 1 year after amputation. For many of these cases, local infiltration of botox into the affected muscle stopped the myoclonus. Our case is only the second reported cause of peripheral myoclonus in the lower extremity.

References: 1. Tyvaert L, Krystkowiak P, Cassim F, Houadyer E, Kreisler A, Destee A, and Defebvre L. Myoclonus of Peripheral Origin: Two Case Reports. Movement Disorders. Vol. 24, No. 2, 2009, pp. 274-300. 2008 Movement Disorder Society. 2. Rath JJ, Tavy DL, Snoeck-Streef I, Contarino MF. Sustained remission of segmental myoclonus due to peripheral nerve injury after treatment with onabotulinumtoxinA. Parkinsonism Relat Disord. 2015 Sep;21(9):1111-2. 3. Uptodate. Myoclonus. 4. Marsden CD,Hallett M,Fahn S. The nosology and pathophysiology of myoclonus. In: MarsdenC,FahnS, editors. Movement disorders. London: Butterworth; 1982. p 196–248. 5. Halliday A The electrophysiological study of myoclonus in man. Brain 1967; 90: 241–284. 6. Hoehn M, Cherington M. Spinal myoclonus. Neurology 1977; 27: 942–946. 7. Shivapour E, Teasdall R. Spinal myoclonus with vacuolar degeneration of anterior horn cells. Arch Neurol 1980; 37: 451–453. 8. Glocker FX, Deuschl G, Volk B, Hasse JJ, and Lucking CH. Bilateral Myoclonus of the Trapezius Muscles After Distal Lesion of an Accessory Nerve. Movement Disorders. Vol. 11, No.5, 1996, pp. 571-575.

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