What causes a bruise across the back?

What Causes a Bruise Across the Back

A bruise across the back in a child is highly concerning for non-accidental trauma and requires immediate evaluation, while in adults the differential includes trauma, bleeding disorders, medications, and underlying medical conditions. 1

Critical Context-Dependent Evaluation

In Children (Especially Non-Mobile Infants)

Bruising on the back is an atypical location for accidental injury and raises significant concern for child abuse. 2

• Location matters critically: Bruising on the buttocks, upper arms, back of legs, or back is rarely observed in unintentional childhood injuries 2
• Pattern recognition: Linear or "tramline" bruises across the back suggest impact from an object such as a belt, cord, or similar weapon 3
• Age considerations: In non-mobile infants, any bruising that cannot be explained by normal handling or pressure sites should prompt evaluation for both abuse and bleeding disorders 1

When to Suspect Non-Accidental Trauma

The American Academy of Pediatrics identifies specific factors that strongly suggest abuse: 1

• Abusive object or hand-patterned bruising (e.g., linear marks, loop marks, grab marks) 1
• History inconsistent with injury: The caregiver's description does not sufficiently explain the bruising pattern or severity 1
• Multiple bruises from a single alleged mechanism: Unintentional injuries typically produce a single bruise (81.7% of cases) 2
• Absence of independent witness: No verifiable trauma history from the child or independent observer 1

When to Evaluate for Bleeding Disorders

The American Academy of Pediatrics provides clear guidance on when bleeding disorder evaluation is NOT needed: 1

• The caregiver's trauma description sufficiently explains the bruising 1
• The child or independent witness provides a history of trauma (abusive or non-abusive) that explains the findings 1
• Abusive patterned bruising is clearly present 1

However, evaluation for bleeding disorders IS warranted when: 1

• History and physical examination do not adequately explain the bruising 1
• There is a family history of bleeding disorders 4, 5
• The child has other bleeding symptoms (mucosal bleeding, excessive bleeding from minor cuts, petechiae) 1
• Medications or alternative therapies that increase bleeding risk are being used 1

Bleeding Disorders That Can Cause Back Bruising

Most Common Inherited Disorders

• Von Willebrand disease: Most common inherited bleeding disorder (prevalence 1 in 1,000), presents with easy bruising and mucocutaneous bleeding, but is NOT detected by standard PT/aPTT screening 4, 5
• Hemophilia (Factor VIII or IX deficiency): Can cause significant bruising even with mild deficiencies, but primarily affects males 4
• Platelet function disorders: Present with bruising despite normal platelet counts, require specialized testing 4
• Factor XIII deficiency: Causes significant bruising but is not detected by PT/aPTT 4

Acquired Causes

• Vitamin K deficiency: Particularly in infants who did not receive prophylaxis at birth, presents with prolonged PT 4
• Immune thrombocytopenia (ITP): Transient disorder with low platelet count 4
• Liver disease/cirrhosis: Decreased clotting factor production 4
• Medications: Anticoagulants, antiplatelets, NSAIDs, steroids, SSRIs (fluoxetine can cause bruising through platelet dysfunction) 6

In Adults

Traumatic Causes

• Direct impact: Fall onto back, assault, sports injury 7
• Deep muscle bruising: Results from forceful trauma causing muscle fiber tearing and hemorrhage 7

Medical Causes

• Senile purpura: Thinning of blood vessels and skin with aging 4
• Medication-induced: Anticoagulants, antiplatelets, SSRIs, corticosteroids 4, 6
• Underlying bleeding disorders: Same as pediatric population but may present later in life 8
• Liver disease: Impaired clotting factor synthesis 4

Diagnostic Approach

Initial Laboratory Testing (When Indicated)

The American Academy of Pediatrics recommends: 1, 4

• Complete blood count with platelet count 4
• Prothrombin time (PT) and activated partial thromboplastin time (aPTT) 1, 4
• Fibrinogen level 4

Critical Pitfall to Avoid

Normal PT/aPTT does NOT rule out bleeding disorders - these tests miss von Willebrand disease, Factor XIII deficiency, and platelet function disorders 4

When Specialized Testing Is Needed

• Von Willebrand disease testing: VWF antigen, VWF ristocetin cofactor activity, Factor VIII levels 4, 5
• Platelet function studies: Light transmission aggregometry, PFA-100 1, 4
• Hematology referral: Required for complex cases or when specialized testing is needed 4

Immediate Action Required

In children with unexplained bruising across the back, consultation with a child abuse pediatrician should be considered in complex or concerning cases. 1 The evaluation for medical conditions should occur simultaneously with evaluation for abuse, as the presence of a bleeding disorder does not rule out abuse, and vice versa. 1