What is the appropriate evaluation and management for a 14‑month‑old infant with a purple discoloration limited to one leg?

Purple Discoloration in One Leg in a 14-Month-Old Child

Immediate Action Required

This 14-month-old child requires urgent evaluation for both life-threatening vascular emergencies and potential child abuse, with immediate assessment of perfusion, complete blood count with platelet count, and skeletal survey if abuse is suspected based on bruising characteristics. 1, 2

Critical Differential Diagnosis Framework

Life-Threatening Vascular Emergencies (Rule Out First)

• Purpura fulminans presents with rapidly progressive purpuric skin lesions, fever, hypotension, and disseminated intravascular coagulation, requiring immediate resuscitation with Ringer's lactate, correction of clotting parameters with heparin, and monitoring for compartment syndrome. 3, 4

• Limb gangrene from thrombotic complications can occur with protein C or protein S deficiency, presenting as extensive thrombosis of venules and capillaries with massive venous outflow obstruction. 5, 4

• Assess limb perfusion immediately: check pulses, capillary refill, temperature, and sensation to rule out arterial occlusion or compartment syndrome requiring emergent fasciotomy. 3

Hematologic Causes Requiring Urgent Laboratory Evaluation

• Obtain complete blood count with platelet count, peripheral blood smear, PT, and aPTT immediately to evaluate for thrombocytopenia, platelet dysfunction, or coagulation factor deficiency. 5, 2

• Immune thrombocytopenic purpura (ITP) typically presents with petechiae and purpura in multiple locations, not isolated to one leg, but must be excluded given the age group. 5

• If platelet count is severely low (<20 × 10⁹/L) with active bleeding, administer platelet transfusions and consider IVIg (0.8-1 g/kg) or corticosteroids (prednisone 4 mg/kg/d for 3-4 days). 5

Child Abuse Evaluation (Mandatory at This Age)

• For a 14-month-old, skeletal survey is necessary if bruising occurs on the upper leg, especially if there is no trauma history or only rough play reported. 1

• Purple discoloration isolated to one leg in a newly mobile toddler is concerning because this location has higher specificity for abuse compared to bony prominences like shins or knees. 5, 1

• Document the exact location, pattern, and size of the discoloration photographically, as bruise appearance changes rapidly and may indicate underlying fractures or deeper tissue injury. 5, 1

• Skeletal survey is mandatory if there is witnessed or confessed abuse, history of domestic violence, patterned bruising (belt marks, hand prints), or additional injuries such as burns or frenulum tears. 5, 1

Age-Specific Risk Stratification for This 14-Month-Old

High-Risk Features Requiring Skeletal Survey

• Bruising on the upper leg (thigh) without clear accidental trauma history. 1
• Any bruising on torso, hand, foot, neck, or ear regardless of explanation. 1
• Patterned appearance suggesting object or hand imprint. 5, 1
• Child is not yet walking independently (developmental delay increases abuse risk). 5

Lower-Risk Features (May Not Require Skeletal Survey)

• Single bruise on shin, knee, or other bony prominence of lower leg with consistent accidental history (playground fall, bumping into furniture). 1
• Child is actively cruising or walking, making accidental leg bruising more plausible. 5
• No additional concerning injuries on full body examination. 1

Specific Diagnostic Algorithm

Step 1: Assess for Emergency (First 15 Minutes)

• Check vital signs for fever, hypotension, or tachycardia suggesting sepsis or purpura fulminans. 3, 4
• Examine affected leg for warmth, pulses, capillary refill, and compartment firmness. 3
• Perform rapid full-body skin examination for additional purpuric lesions, petechiae, or signs of systemic involvement. 2, 6

Step 2: Obtain Immediate Laboratory Studies

• Complete blood count with platelet count and peripheral smear. 5, 2
• PT and aPTT to evaluate coagulation cascade. 2
• If purpura fulminans suspected: add fibrinogen, D-dimer, protein C/S levels. 4

Step 3: Determine Need for Skeletal Survey

• If bruising is on upper leg (thigh), hand, foot, torso, neck, or ear → skeletal survey is necessary. 1
• If bruising is only on shin/knee with clear accidental history and child is walking → skeletal survey may be inappropriate. 1
• If child is under 12 months or non-mobile → skeletal survey is mandatory regardless of location. 1

Step 4: Consider Bleeding Disorder Workup

• Obtain bleeding disorder evaluation if bruising is disproportionate to reported trauma, there are multiple bruises in unusual locations, or there is personal/family history of bleeding symptoms. 1, 2

Critical Pitfalls to Avoid

• Never dismiss unilateral leg discoloration as simple bruising without excluding vascular emergency, as purpura fulminans can progress to gangrene requiring amputation within hours. 3, 4

• Do not assume mobility explains bruising in a 14-month-old without careful location assessment, as bruising on the thigh (upper leg) remains highly suspicious even in mobile toddlers. 1

• Failure to perform skeletal survey when indicated can miss occult fractures that predict future severe abuse including fatal head trauma. 5

• Do not wait for laboratory results before initiating resuscitation if the child appears ill with fever and progressive purpura, as purpura fulminans requires immediate heparin and fresh frozen plasma. 3, 4