Postsurgical Myoclonus of the Pectoralis Major

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Case Description

A 52‐year‐old woman diagnosed with invasive mammary carcinoma in the left breast was submitted to skin‐sparing mastectomy followed by adjuvant chemotherapy and radiotherapy and prosthetic breast reconstruction. One month after implant placement, a breast infection prompted its removal. A few days later, she developed burning pain and intermittent, involuntary movements in the left pectoralis major muscle. Movements subsided during sleep. Electromyography showed rhythmic and irregular activity in the pectoralis major muscle lasting less than 200 milliseconds without doublets or triplets motor unit discharges. Cervical spine magnetic resonance imaging was normal. Clonazepam was ineffective. Local anesthesia of the medial and lateral pectoral nerves resulted in partial and temporary resolution of the symptoms. She is now being evaluated to undergo a left pectoral neurectomy (Video S1).

What is the most likely movement shown in the video?

1. Myoclonus

2. Myokymia

3. Fasciculations

4. Tremor

Answer

Pectoralis major myoclonus secondary to subpectorial breast implant removal is a form of spontaneous myoclonic jerks associated with local nerve irritation. The elevation, mobilization, and distension of the pectoralis major muscle and the resulting tension on the medial and/or lateral pectoral nerves probably explain the pathophysiology of these muscle spasms. The pectoralis major muscle is dually innervated and a submuscular implant may potentially transect the medial pectoral nerve as it courses through the pectoralis minor muscle on its way to innervate the major muscle. If one of the nerves remains intact but injured, it may lead to the development of myoclonus. ¹ This is an example of a peripheral movement disorders, mostly represented by hemifacial spasms in clinical practice. Another less common example includes jumpy stump. A common pathophysiology composed of the peripheral compression of the nerve and afferent aberrant signaling to the central structures might explain the peripheral movement disorders.

Tetanic spasms of the pectoralis major muscle were first described in a patient after sternal wound reconstruction and has subsequently been described after tissue expander based breast reconstruction. These patients exhibit visible myoclonic contractions with severe pain. ² Our patient developed the spasms after the implant removal. Historically, infiltrations of botulinum toxin type A into the muscle was the initial treatment option, but with only immediate and temporary relief. Another potential treatment option, offered to our patient, is pectoral neurectomies because there are reports of excellent outcomes with the relief of spasms and pain. ¹

One might think of this movement disorder being functional, but our patient's movement was not inconsistent, distractible, or increased with observation, and we have not found entrainment or suggestibility in the evaluations.

Author Roles

(1) Case Report Project: A. Conception, B. Organization, C. Execution; (2) Data Collection: A. Case Report; (3) Manuscript Preparation: A. Writing of the First Draft, B. Review and Critique.

T.G.d.P.: 1A, 1B, 2A, 3A

T.C.V.: 1A, 1B, 1C, 3A, 3B

J.L.P.: 1A, 1B, 1C, 3A, 3B

O.G.P.B.: 1A, 1B, 1C, 2A, 3A, 3B

Disclosures

Ethical Compliance Statement: The authors confirm that the approval of an institutional review board was not required for this work. Informed consent was obtained. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines.

Funding Sources and Conflict of Interest: No specific funding was received for this work. We declare no conflicts of interest for this work.

Financial Disclosures for the previous 12 months: The authors declare that there are no additional disclosures to report.

Supporting information

Video S1 Myoclonus of the left pectoralis major muscle.