What is the differential diagnosis (ddx) for a 34-year-old female with left axillary pain?

Differential Diagnosis for Left Axillary Pain in a 34-Year-Old Female

The differential diagnosis for left axillary pain in a 34-year-old woman includes axillary lymphadenopathy (reactive, malignant, or silicone-related), axillary web syndrome, intercostobrachial nerve injury, scapulothoracic bursitis with referred pain, and upper thoracic radiculopathy.

Primary Diagnostic Categories

Axillary Lymphadenopathy

This represents the most common structural cause requiring systematic evaluation:

• Reactive lymphadenopathy from infections is the most frequent benign etiology, including recent viral illnesses, skin infections, or cat-scratch disease 1
• Metastatic breast cancer is the most common malignant cause when cancer is identified in axillary nodes, though occult breast cancer with axillary metastases occurs in less than 1% of breast cancers 1
• Lymphoma (particularly non-Hodgkin's lymphoma) can present with unilateral axillary adenopathy and requires consideration if nodes are firm, fixed, or progressively enlarging 1
• Silicone adenitis from breast implants (if present) produces characteristic "snowstorm" appearance on ultrasound and can cause painful adenopathy 1, 2

Musculoskeletal and Neurologic Causes

• Axillary web syndrome occurs in approximately 50% of women following breast cancer surgery and presents as a tight band of tissue in the axilla, though it can develop spontaneously; it persists for 18 months or longer and is associated with reduced shoulder range of motion 3
• Scapulothoracic bursitis represents a significant but underrecognized cause, with 78.6% of affected patients presenting with breast/chest wall as the primary site of discomfort despite the pathology originating at the medial scapular border; 83.5% achieve complete pain relief with corticosteroid injection at the point of maximum tenderness 4
• Intercostobrachial nerve injury causes neuropathic pain in the axilla and inner upper arm, typically following axillary surgery but can occur from other trauma 5
• Upper thoracic radiculopathy (T1-T2) can present with axillary pain and may indicate neoplastic involvement if pain is severe or progressive 6

Initial Clinical Assessment Algorithm

History Elements to Elicit

• Recent infections, vaccinations, or trauma to assess for reactive adenopathy 2
• Breast implant history as implants cause benign lymphadenopathy and silicone adenitis 1, 2
• Prior breast cancer surgery as 27.2% of scapulothoracic bursitis cases have this history 4
• Pain characteristics: focal versus diffuse, relationship to shoulder movement, presence of palpable cord-like structures, radiation pattern 2, 7
• Associated symptoms: palpable mass, skin changes, shoulder range of motion limitations, paresthesias 8, 7

Physical Examination Specifics

• Palpate for discrete axillary masses versus diffuse adenopathy versus cord-like structures 8, 2
• Assess for trigger point at medial scapular border by having patient reach across body; tenderness here suggests scapulothoracic bursitis 4
• Test shoulder range of motion, particularly abduction, as limitation with visible/palpable cord suggests axillary web syndrome 3
• Examine for sensory changes in axilla and medial upper arm distribution (intercostobrachial nerve territory) 5
• Perform thorough breast examination for masses, asymmetric thickening, nipple discharge, or skin changes 8

Imaging Algorithm Based on Age and Findings

For This 34-Year-Old Patient

If palpable axillary mass or lymphadenopathy is present:

• Ultrasound is the initial and primary examination for patients under 30-40 years of age 8, 2
• Characterize cortical thickness, uniformity, size, shape, and vascularity pattern on ultrasound as these features predict malignancy 2
• Look for "snowstorm" appearance indicating silicone adenitis if implants are present 8, 2

If imaging shows morphologically abnormal lymph nodes:

• Ultrasound-guided core needle biopsy is preferred over fine needle aspiration for definitive diagnosis 2
• If biopsy shows metastatic breast cancer but no breast primary is evident, obtain breast MRI with contrast to identify occult primary 8

If imaging is negative/benign but symptoms persist:

• Consider observation with clinical follow-up or repeat imaging in 4-6 weeks if symptoms worsen 2
• Evaluate for musculoskeletal causes with focused physical examination 4

Additional Imaging Considerations

• PET/CT should be considered if there is concern for lymphoma or other non-breast malignancy 2
• MRI of cervical and upper thoracic spine if neurologic symptoms suggest radiculopathy, particularly if pain is severe or progressive 6

Critical Pitfalls to Avoid

• Do not dismiss focal axillary pain as benign without imaging in women of childbearing age, as the risk of cancer in isolated breast/axillary pain is 1.2-6.7% 8
• Do not overlook referred pain from scapulothoracic bursitis, which presents as breast/chest wall pain in 78.6% of cases despite the pathology being at the scapula 4
• Do not assume bilateral adenopathy excludes breast cancer, as systemic processes are more common but breast cancer can present with bilateral nodes 1
• Recognize that severe or progressive axillary pain may indicate upper thoracic root neoplasm and warrants spine imaging if other causes are excluded 6