Can radiation therapy for breast cancer worsen a pre-existing brachial plexus injury?

Radiation Therapy Can Worsen Pre-existing Brachial Plexus Injury in Breast Cancer Patients

Yes, radiation therapy for breast cancer can worsen a pre-existing brachial plexus injury, particularly when radiation doses exceed 50 Gy or when using larger fraction sizes. 1

Mechanism and Risk Factors

Radiation therapy can cause additional damage to an already compromised brachial plexus through several mechanisms:

• Radiation-induced fibrosis: Progressive scarring of nerve tissue can exacerbate existing nerve damage
• Microvascular damage: Radiation causes ischemia to the nerves, potentially worsening pre-existing injury
• Oxidative stress and inflammation: These processes can compound existing neural damage

Key risk factors that increase the likelihood of worsening a pre-existing injury include:

• Higher radiation doses: Particularly doses exceeding 50 Gy 1
• Larger fraction sizes: Fractions of 2 Gy or less are recommended to minimize risk 1, 2
• Concurrent chemotherapy: Cytotoxic therapy adds to the damaging effect of radiotherapy 2
• Younger patient age: Peripheral nerves in younger patients appear more vulnerable 2
• Radiation field location: Treatment that includes the axillary and/or supraclavicular regions 3

Clinical Presentation of Worsening

When radiation therapy worsens a pre-existing brachial plexus injury, patients typically experience:

• Progressive sensory symptoms: Paresthesia (100%), hypaesthesia (74%), and pain (47%) 2
• Motor deficits: Weakness (58%) that often progresses from distal to proximal 3
• Reflex changes: Decreased muscle stretch reflexes (47%) 2
• Delayed onset: Symptoms may develop months to years after radiation treatment 1, 3

Diagnostic Approach

To differentiate between radiation-induced worsening versus tumor recurrence:

• MRI of the brachial plexus: With and without contrast is the most accurate imaging method 4, 1
• FDG-PET/CT: Beneficial to differentiate radiation plexitis from tumor recurrence 1
• Clinical pattern: Radiation-induced damage typically occurs as diffuse damage to the brachial plexus 2

Management Options

For patients with worsened brachial plexus injury after radiation:

• Pain management: Multimodal pain control strategies for neuropathic pain
• Surgical interventions: Omentoplasty may be considered for refractory pain cases, though patients must be informed about the risk of motor function deterioration 1, 5
• External neurolysis: May be recommended in patients with severe clinical manifestations 6
• Emerging treatments: Therapies targeting radiation-induced fibrosis, ischemia, oxidative stress, and inflammation show promise, including pentoxifylline, tocopherol, and clodronate (PENTOCLO) 1

Prevention Strategies

To minimize risk when radiation therapy is needed in patients with pre-existing brachial plexus injury:

• Dose reduction: Lower radiation dose to the supraclavicular region 1
• Field modification: Exclude the axillary region from treatment when possible 1
• Modern techniques: Use precise targeting and fractions of 2 Gy or less 1, 2

Important Considerations

• Radiation-induced worsening may be misdiagnosed as tumor recurrence, making accurate imaging crucial 6
• The incidence of radiation-induced brachial plexopathy has decreased with improved radiation techniques but remains a significant concern 5
• Long-term follow-up is essential as symptoms may develop decades after treatment 3

Careful radiation planning and monitoring are essential when treating breast cancer patients with pre-existing brachial plexus injuries to minimize the risk of exacerbating their condition.