What could be causing bilateral arm pain with abduction at 90° and lumps under the arm after a possible episode of bronchitis or pneumonia?

Bilateral Arm Pain with Abduction and Axillary Lumps Following Respiratory Infection

This clinical presentation most likely represents reactive lymphadenopathy causing musculoskeletal pain during arm abduction, secondary to a recent respiratory infection (bronchitis or pneumonia), and requires urgent evaluation to exclude pneumonia and assess for complications.

Immediate Diagnostic Priorities

The most critical first step is distinguishing between uncomplicated bronchitis versus pneumonia, as this fundamentally changes management and prognosis:

• Obtain a chest radiograph immediately if any of the following are present: heart rate >100 beats/min, respiratory rate >24 breaths/min, oral temperature >38°C, or chest examination findings of focal consolidation, egophony, or fremitus 1
• The absence of all four findings above reduces pneumonia likelihood sufficiently to potentially obviate chest imaging, but given the presence of axillary lumps (suggesting possible complications), imaging is still warranted 1
• Pneumonia must be ruled out because it carries significant morbidity and mortality when inadequately treated, particularly in vulnerable populations 1, 2

Most Likely Diagnosis

Reactive axillary lymphadenopathy from the respiratory infection is the most probable cause of the "lumps under arm":

• Respiratory infections commonly cause regional lymph node enlargement as part of the immune response 2
• The bilateral arm pain with abduction at 90° likely represents mechanical irritation or inflammation of the enlarged axillary lymph nodes being compressed during this movement
• This pain pattern is consistent with lymph node involvement rather than primary musculoskeletal pathology

Critical Differential Diagnoses to Exclude

Pneumonia with Complications

• Pneumonia can present with extrapulmonary manifestations including lymphadenopathy 3, 2
• Bacterial superinfection following viral bronchitis occurs because viral infections impair mucociliary clearance and bacterial killing by pulmonary macrophages 1
• Common bacterial pathogens include Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis 1

Atypical Pneumonia

• Mycoplasma pneumoniae and Chlamydophila pneumoniae can cause pneumonia with prominent extrapulmonary manifestations including arthralgias and lymphadenopathy 3
• These pathogens should be considered, especially if the clinical course is atypical 1

Influenza with Systemic Symptoms

• Influenza commonly presents with fever, cough, and myalgias/arthralgias that could mimic the bilateral arm pain 3
• RSV in adults can cause intense coughing with systemic symptoms 3

Diagnostic Workup

Physical examination should specifically assess:

• Palpation of axillary lymph nodes for size, consistency, mobility, and tenderness
• Chest auscultation for focal consolidation, egophony, or fremitus 1
• Vital signs including heart rate, respiratory rate, and temperature 1

Laboratory and imaging:

• Chest radiograph to identify infiltrates or pleural effusion 1, 3
• Blood cultures if pneumonia is suspected, particularly in high-risk patients 1
• Sputum culture is generally not indicated for uncomplicated acute bronchitis 1

Management Approach

If Pneumonia is Excluded (Acute Bronchitis Only)

Antibiotics are NOT routinely indicated for uncomplicated acute bronchitis in immunocompetent adults:

• The American College of Chest Physicians recommends against routine antibiotic use, as most cases are viral 3
• Antibiotics should only be considered if the condition worsens and bacterial superinfection is suspected 3
• Symptomatic treatment is appropriate with reassessment if symptoms persist beyond 48-72 hours 3

If Pneumonia is Confirmed

Immediate antibiotic therapy is required:

• Amoxicillin is the reference treatment for pneumococcal pneumonia 1
• Consider broader spectrum coverage (amoxicillin-clavulanate, fluoroquinolone active against pneumococcus) if risk factors are present 1
• Treatment duration is typically 14 days with clinical reassessment within 3 days 1

Critical Pitfalls to Avoid

• Do not assume purulent sputum indicates bacterial infection requiring antibiotics, as sputum color alone does not reliably predict bacterial etiology 3
• Do not miss pneumonia by failing to obtain chest radiography when fever and productive cough are present with systemic symptoms 3
• Do not overlook serious complications such as empyema or pleural effusion that could explain the axillary symptoms 1
• Consider that recurrent episodes may represent underlying asthma rather than repeated infections, as approximately one-third of patients with acute cough are misdiagnosed 1, 3

Follow-up Considerations

• If symptoms persist beyond 3 weeks, consider alternative diagnoses including postinfectious cough, upper airway cough syndrome, asthma, or gastroesophageal reflux disease 1
• Axillary lymphadenopathy should resolve as the respiratory infection clears; persistent or enlarging nodes warrant further investigation
• Reassess within 48-72 hours if treated empirically to ensure clinical improvement 3