What is the diagnosis and treatment approach for a patient presenting with symptoms suggestive of Parsonage-Turner syndrome, characterized by sudden onset of severe pain in the shoulder and arm, followed by weakness and atrophy of the muscles?

Parsonage-Turner Syndrome: Diagnosis and Management

Clinical Presentation and Diagnosis

Parsonage-Turner syndrome (PTS), also known as neuralgic amyotrophy or idiopathic brachial plexopathy, presents with sudden onset of severe unilateral shoulder pain followed within hours to days by progressive weakness, muscle atrophy, and dysesthesias in the affected upper extremity. 1, 2

Key Diagnostic Features

• Acute severe shoulder and arm pain that develops abruptly, typically unilateral, representing the initial and most prominent symptom 1, 2
• Progressive weakness and early muscle atrophy appearing within hours to several days after pain onset, affecting shoulder and upper arm muscles 1, 3
• Patchy neurologic deficits including weakness, paresthesias, and numbness that do not follow a single nerve root distribution 2, 4
• Commonly affected muscles include supraspinatus, infraspinatus, teres minor and major, trapezius, and serratus anterior 5
• Phrenic nerve involvement occurs frequently, causing diaphragmatic dysfunction that can be detected by diaphragm ultrasound 1

Diagnostic Workup

• MRI imaging demonstrates multifocal T2 hyperintensities in affected nerves and muscles, with characteristic nerve hourglass swellings and constrictions 1, 5
• Ultrasound can identify nerve hourglass swellings and constrictions, providing complementary diagnostic information 1
• Electrodiagnostic testing assists in distinguishing PTS from cervical radiculopathy, rotator cuff pathology, and other mimicking disorders 1, 4
• Exclude alternative diagnoses including malignancy, hypereosinophilic syndrome, and rheumatologic conditions through appropriate laboratory testing 5

Etiology and Triggers

• Inflammatory immune component is suggested by nerve biopsy findings and common triggering events 1
• Common triggers include recent viral infections (most common), immunizations, trauma, surgery, and childbirth 1, 5, 2
• COVID-19 association has been documented as a precipitating viral infection 5
• Hereditary form (HBPN) caused by dominant SEPT9 mutations presents identically to idiopathic PTS but features recurrent attacks 1

Treatment Approach

Acute Phase Management

• High-dose pulsed corticosteroids should be administered for initial severe pain control 1
• Non-narcotic pain medications are preferred for ongoing pain management, as weakness and subsequent pain do not clearly respond to steroids 1
• Physical therapy should be initiated early, focusing on restoring functional scapular mechanics, preventing contractures, and energy conservation 1

Long-Term Management

• Time and rehabilitation are the primary treatments, as most patients make dramatic functional recovery without aggressive interventions 1, 3
• Tendon transfers should be considered only when recovery does not occur after 18 months of conservative management 1
• Early neurolysis and nerve grafts remain controversial and are not routinely recommended 1

Prophylaxis for Hereditary Form

• Prophylactic corticosteroids or intravenous immunoglobulin may reduce surgical- or childbirth-induced attacks in patients with documented HBPN 1

Prognosis

• Recovery is usually complete with most patients achieving dramatic functional improvement over time 1, 3
• Recovery timeline can extend beyond 3 years from onset, requiring patient counseling about prolonged rehabilitation 1
• Lifetime residual pain and weakness are rare outcomes 1
• Recurrence rate in hereditary forms is common, while idiopathic PTS typically follows a monophasic course 1

Critical Pitfalls to Avoid

• Delayed diagnosis occurs when symptoms are attributed to rotator cuff pathology, cervical radiculopathy, or postoperative positioning effects rather than recognizing the characteristic pain-then-weakness pattern 2, 4
• Misattribution in postoperative patients where PTS symptoms may be incorrectly ascribed to surgical positioning, anesthetic block complications, or normal postoperative recovery 2
• Overlooking phrenic nerve involvement which requires specific assessment with diaphragm ultrasound 1
• Premature surgical intervention before allowing adequate time (18 months minimum) for spontaneous recovery 1