What could be causing a swollen and bruised arm in an elderly patient with normal coagulation studies (prothrombin time (PT) 11.9, international normalized ratio (INR) 1.1, activated partial thromboplastin time (aPTT) 29) and no evidence of blood clots on ultrasound?

Swollen and Bruised Arm in Elderly Patient: Diagnostic Approach

Given normal coagulation studies and negative ultrasound for DVT, the most likely causes are trauma-related soft tissue injury (even if not recalled), compartment syndrome, or inflammatory conditions such as polymyalgia rheumatica or vasculitis, and you should immediately assess for compartment syndrome and consider inflammatory markers (ESR/CRP) along with referral to rheumatology or vascular surgery depending on clinical findings.

Immediate Assessment Priorities

Rule Out Compartment Syndrome

• Assess the 5 P's immediately: Pain (especially with passive stretch), Pressure (tense compartment), Paresthesias, Pallor, and Pulselessness 1, 2
• Compartment syndrome can occur spontaneously in elderly patients, particularly those on anticoagulants or with minor unrecognized trauma
• If any signs are present, this requires urgent surgical consultation for potential fasciotomy

Verify Coagulation Status is Truly Normal

Your coagulation studies (PT 11.9, INR 1.1, aPTT 29) are reassuringly normal and effectively rule out most coagulopathies 3

• However, these tests only assess 4% of thrombin production and may miss platelet dysfunction 3
• Normal PT and aPTT with bruising suggests a platelet disorder or vascular problem rather than a clotting factor deficiency 1, 2

Additional Laboratory Testing Needed

First-Line Additional Tests

• Complete Blood Count (CBC) with platelet count: Essential to evaluate for thrombocytopenia or other hematologic abnormalities 4, 1, 2
• Inflammatory markers (ESR and CRP): Critical given the combination of swelling and potential morning stiffness in an elderly patient, as this pattern suggests inflammatory conditions like polymyalgia rheumatica 4
• Peripheral blood smear: Can identify platelet abnormalities or hematologic disorders not apparent on automated counts 5, 1

Consider if Initial Tests Abnormal

• Fibrinogen level: Only if coagulation abnormalities emerge, as it assesses for consumptive coagulopathy 4
• Liver function tests: Only necessary if coagulation tests become abnormal, as liver dysfunction affects clotting factor production 4

Tests NOT Indicated

• Lupus anticoagulant, Factor V Leiden, Prothrombin gene mutation: These evaluate thrombotic disorders, not bleeding/bruising, and are inappropriate here 4
• Protein C/S testing: Only indicated with thrombosis history, not bruising 4

Differential Diagnosis to Consider

Most Likely Causes

1. Occult trauma with soft tissue injury: Elderly patients may not recall minor trauma due to cognitive issues or nocturnal injury
2. Inflammatory conditions:
   • Polymyalgia rheumatica (bilateral limb involvement with morning stiffness is classic) 4
   • Vasculitis (can present with limb swelling and purpura)
3. Spontaneous hematoma: Can occur in elderly even without significant coagulopathy due to vessel fragility
4. Medication-related: Even with normal coagulation studies, antiplatelet agents (aspirin, clopidogrel) or NSAIDs can cause significant bruising 3, 1

Less Common but Important

• Compartment syndrome: As noted above, requires immediate recognition
• Venous insufficiency with dependent edema and stasis changes: Though ultrasound was negative for DVT
• Angioedema: Usually involves face but can affect extremities

Referral Recommendations

Immediate Referral (Same Day)

• Vascular surgery or emergency department if any signs of compartment syndrome are present
• Emergency department if patient develops systemic symptoms, progressive swelling, or neurovascular compromise

Urgent Referral (Within Days)

• Rheumatology if inflammatory markers (ESR/CRP) are significantly elevated, suggesting inflammatory arthritis or polymyalgia rheumatica 4
• Hematology if CBC shows thrombocytopenia, abnormal cells on smear, or if bleeding assessment tool suggests underlying bleeding disorder 1, 2

Routine Referral (Within Weeks)

• Vascular surgery if chronic venous insufficiency is suspected
• Geriatrics for comprehensive evaluation if cognitive impairment is preventing accurate history

Clinical Pitfalls to Avoid

• Don't assume normal PT/INR and aPTT rule out all bleeding disorders: These tests miss platelet dysfunction and von Willebrand disease, which are common causes of bruising with normal coagulation studies 3, 5, 1
• Don't overlook medication history: Carefully review ALL medications including over-the-counter NSAIDs, aspirin, and herbal supplements that can affect bleeding 3, 1
• Don't dismiss the patient's denial of trauma: Elderly patients may have unwitnessed falls, nocturnal injuries, or cognitive impairment affecting recall 2
• Don't delay assessment for compartment syndrome: This is a surgical emergency and clinical diagnosis should not wait for additional testing 1
• Don't order excessive coagulation testing without clinical indication: Tests like lupus anticoagulant and thrombophilia panels are for thrombosis evaluation, not bruising, and lead to unnecessary costs and false positives 4

Monitoring Plan

• Serial examinations: Reassess the arm every 4-6 hours initially for progression of swelling or development of compartment syndrome
• Document neurovascular status: Pulses, sensation, motor function, and compartment tension
• Photograph the affected area: Useful for tracking progression and for specialist consultation 2
• If inflammatory markers are elevated, consider a trial of corticosteroids after rheumatology consultation, as polymyalgia rheumatica responds dramatically to low-dose prednisone 4