Working Diagnosis:
Pectoralis minor syndrome and neurogenic thoracic outlet syndrome ("double crush syndrome")

Treatment:
The patient underwent image-guided botulinum toxin injections to both the anterior scalene and pectoralis minor muscles, resulting in immediate and significant symptom relief.

Outcome:
The patient returned to all activities without restriction following botulinum toxin injections and continued physical therapy.

Future management may include repeat botulinum toxin injections or surgical intervention if symptoms recur.

Author's Comments:
Positive diagnostic neuromuscular blocks and subsequent symptom recurrence after anesthetic wear-off confirmed the diagnoses of neurogenic thoracic outlet syndrome and pectoralis minor syndrome, together known as double crush syndrome.

Thoracic outlet syndrome is a neurovascular compression disorder that may cause pain, paresthesia, weakness, and functional impairment of the upper extremity. Compression most commonly occurs within the scalene triangle or costoclavicular space, whereas infraclavicular compression at the pectoralis minor is less common.

This case demonstrated dual sites of neural compression involving both the anterior scalene and pectoralis minor regions. Diagnostic neuromuscular blockade proved critical in localizing the sites of compression and establishing the diagnosis.

Editor's Comments:
This case highlights the importance of maintaining a broad differential diagnosis in patients with persistent shoulder and upper extremity symptoms when routine orthopedic evaluation and imaging are unrevealing.

Thoracic outlet syndrome and pectoralis minor syndrome can present with overlapping symptoms, including pain, paresthesia, weakness, and functional limitation. As demonstrated in this case, physical examination findings helped localize potential sites of neurovascular compression and guided subsequent diagnostic interventions.

Diagnostic neuromuscular blocks played an important role in confirming the diagnosis. Partial relief following the anterior scalene block suggested thoracic outlet syndrome, while near-complete symptom resolution after pectoralis minor blockade identified a second site of compression. The combination of these findings supported the diagnosis of double crush syndrome and informed successful treatment with botulinum toxin injections.

Clinicians should consider thoracic outlet syndrome and pectoralis minor syndrome in patients with persistent upper extremity symptoms when traditional imaging studies are nondiagnostic and symptoms are reproduced with provocative examination maneuvers.

References:
1. Lim C, Kavousi Y, Lum YW, Christo PJ. Evaluation and Management of Neurogenic Thoracic Outlet Syndrome with an Overview of Surgical Approaches: A Comprehensive Review. J Pain Res. 2021 Oct 5;14:3085-3095. doi: 10.2147/JPR.S282578. PMID: 34675637; PMCID: PMC8502052.

2. Rizzo S, Talei Franzesi C, Cara A, Cassina EM, Libretti L, Pirondini E, Raveglia F, Tuoro A, Vaquer S, Degiovanni S, Cavalli EM, Marchesi A, Froio A, Petrella F. Diagnostic and Therapeutic Approach to Thoracic Outlet Syndrome. Tomography. 2024 Sep 1;10(9):1365-1378. doi: 10.3390/tomography10090103. PMID: 39330749; PMCID: PMC11436167.

3. Woodworth TT, Le A, Miller C, Conger A, Mahan MA, Cushman DM. Botulinum toxin injections for the treatment of neurogenic thoracic outlet syndrome: A systematic review. Muscle Nerve. 2024 Jul;70(1):28-35. doi: 10.1002/mus.28080. Epub 2024 Mar 26. PMID: 38529885.

4. Torriani M, Gupta R, Donahue DM. Botulinum toxin injection in neurogenic thoracic outlet syndrome: results and experience using a ultrasound-guided approach. Skeletal Radiol. 2010 Oct;39(10):973-80. doi: 10.1007/s00256-010-0897-1. Epub 2010 Feb 26. PMID: 20186413

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