What causes petechiae in the arms and legs?

Petechiae in Arms and Legs: Causes and Clinical Approach

Petechiae in the arms and legs can result from life-threatening infections (meningococcemia, Rocky Mountain Spotted Fever), hematologic disorders (immune thrombocytopenia, thrombotic thrombocytopenic purpura), autoimmune conditions, drug reactions, or mechanical trauma—with urgent evaluation required to exclude rapidly progressive bacterial infections that can be fatal within hours. 1, 2

Life-Threatening Infectious Causes (Evaluate First)

Meningococcal Disease

• Neisseria meningitidis causes invasive disease with petechial or purpuric rash that rapidly progresses to purpura fulminans, typically with high fever, severe headache, and altered mental status 2
• The rash can progress extremely rapidly with clinical deterioration occurring within hours 2, 3
• Up to 50% of early meningococcal cases may lack rash initially, so absence of petechiae does not exclude this diagnosis 2

Rocky Mountain Spotted Fever (RMSF)

• The classic petechial rash appears by day 5-6 of illness, beginning as small blanching pink macules on ankles, wrists, or forearms that evolve to maculopapular lesions with central petechiae 1, 2
• Petechial involvement of palms and soles indicates advanced disease and severe illness 1, 2
• Critical pitfall: Up to 20% of RMSF cases completely lack rash, and absence of rash is associated with increased mortality 1, 2
• The classic triad of fever, rash, and tick bite is present in only a minority of patients at initial presentation—do not wait for this triad before considering RMSF 1, 2
• Rash typically appears 2-4 days after fever onset, but most patients seek care before rash develops 1

Other Serious Infections

• Bacterial endocarditis can cause petechiae on palms and soles 1, 2
• Ehrlichiosis (E. chaffeensis) presents with petechiae in approximately one-third of cases, though rash occurs in up to 66% of children 1, 2
• Secondary syphilis (Treponema pallidum), rat-bite fever (Streptobacillus moniliformis), and disseminated gonococcal infection can all cause petechial rashes 1, 2

Hematologic Causes

Immune Thrombocytopenia (ITP)

• ITP presents with easy or excessive bruising, petechiae (usually on lower legs), bleeding from gums or nose, and blood in urine or stool 1
• A 3-year-old child with scattered petechiae and bruises to arms and legs with platelet count of 8 × 10⁹/L represents typical ITP presentation 1
• Diagnosis requires careful history, physical examination, complete blood count, and peripheral blood smear review 1
• Petechiae on limbs with gradually decreasing platelet count and elevated platelet-associated IgG suggests ITP 4

Other Hematologic Disorders

• Thrombotic thrombocytopenic purpura (TTP) causes petechial rash alongside systemic manifestations 1, 2
• Aplastic anemia may present with unexplained or easy bruising, petechiae, and skin rash 1
• Gray platelet syndrome can present with petechiae on limbs and thrombocytopenia 4

Autoimmune and Vasculitic Causes

• Adult-Onset Still's Disease can present with vasculitic purpuric rash, sometimes associated with mixed cryoglobulinemia, characterized by perivascular inflammation with lymphocyte and histiocyte invasion 2, 5

Viral Causes

• Enteroviruses (coxsackievirus, echovirus) can cause petechial rashes that may mimic bacterial causes but typically progress more slowly 2, 3
• Human herpesvirus 6 (roseola), parvovirus B19, and Epstein-Barr virus may present with rashes that include petechial components 2, 3
• Viral petechial rashes are more generalized and less likely to involve palms and soles compared to RMSF 3

Drug-Induced Causes

• Drug hypersensitivity reactions can cause petechial rash on palms and soles 1, 2
• Acute thrombocytopenic purpura with sudden onset of petechiae and ecchymoses has been reported following anti-influenza vaccination 6

Mechanical and Traumatic Causes

• Trauma causing increased capillary pressure can result in petechiae 2, 7
• Well infants with localized petechiae/purpura to lower limbs (often bilateral) without fever likely have benign mechanical etiology such as tourniquet phenomenon from diapers 8
• Mechanical disruption of capillary walls or cellular injury permitting red blood cell transit through endothelial cytoplasm can cause petechiae 7

Critical Clinical Pitfalls to Avoid

Recognition Challenges

• In darker-skinned patients, petechial rashes may be difficult to recognize, increasing risk of delayed diagnosis 1, 2
• Rash on palms and soles is NOT pathognomonic for any single condition—consider RMSF, meningococcemia, secondary syphilis, endocarditis, and drug reactions 1, 2

Diagnostic Errors

• Never dismiss absence of rash: up to 20% of RMSF cases and 50% of early meningococcal cases lack rash 2
• Do not wait for classic presentation features before initiating evaluation for life-threatening causes 1, 2
• Vesicles, bullae, and petechiae developing on inflamed skin with systemic toxicity should prompt consideration of deeper infections like necrotizing fasciitis 1

Evaluation Approach

• For well-appearing infants with localized petechiae to lower limbs and no fever, benign etiology is more likely, but observation for progression is required 8
• Blood culture results are positive in only 5% of cellulitis cases with petechiae, limiting their diagnostic utility in that context 1
• Carefully review blood film results in differential diagnosis of thrombocytopenia, as large hypogranular platelets may indicate conditions like gray platelet syndrome 4