What are the causes of new onset petechiae?

Causes of New Onset Petechiae

New onset petechiae require immediate evaluation for life-threatening infectious causes—particularly meningococcemia and Rocky Mountain Spotted Fever—followed by systematic assessment for hematologic disorders, autoimmune conditions, and mechanical causes.

Life-Threatening Infectious Causes (Evaluate First)

Meningococcemia

• Neisseria meningitidis causes rapidly progressive petechial or purpuric rash that can evolve to purpura fulminans within hours 1
• Presents with high fever, severe headache, altered mental status, and rash that progresses more rapidly than RMSF 1
• Critical pitfall: Up to 50% of early cases lack rash initially—do not wait for complete clinical picture before treatment 2

Rocky Mountain Spotted Fever (RMSF)

• 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
• Petechial involvement of palms and soles indicates advanced disease and severe illness 1, 2
• Critical pitfall: Up to 20% of cases never develop 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 at initial presentation 1
• Rash may be difficult to recognize in darker-skinned patients 1, 2

Other Bacterial Infections

• Infective endocarditis can cause petechiae on palms and soles 1, 2
• Secondary syphilis (Treponema pallidum) may present with petechial rash on palms and soles 1, 2
• Rat-bite fever (Streptobacillus moniliformis) can cause petechial rash 1, 2
• Ehrlichiosis (E. chaffeensis) presents with petechial or maculopapular rash in approximately 30% of adults and 60% of children, appearing median 5 days after illness onset 1

Viral Causes

• Enteroviruses (coxsackievirus, echovirus) can cause petechial rashes that typically progress more slowly than bacterial causes 1, 3
• Human herpesvirus 6 (roseola), parvovirus B19, and Epstein-Barr virus may present with maculopapular rashes with petechial components 1, 2

Hematologic Disorders

Platelet Disorders

• Immune thrombocytopenic purpura (ITP) can present with petechiae as initial manifestation, sometimes limited to oral mucosa before cutaneous signs appear 1, 4
• Requires complete blood count to assess platelet count 1, 3
• In nonmobile infants, bleeding disorders can present with petechiae at clothing line pressure sites or in patterns of object pressure (e.g., infant seat fasteners) 1

Coagulation Disorders

• Thrombotic thrombocytopenic purpura (TTP) causes petechial rash with systemic manifestations 1, 2
• Mild hemophilia (factor VIII or IX deficiency) may not cause aPTT abnormalities but can still result in significant bleeding 1
• Von Willebrand disease and factor XIII deficiency are not reliably detected by PT/aPTT screening 1

Autoimmune and Vasculitic Causes

• Adult-Onset Still's Disease (AOSD) can present with vasculitic purpuric rash, sometimes associated with mixed cryoglobulinemia, characterized by perivascular inflammation with lymphocyte and histiocyte invasion 3, 5
• Kawasaki disease should be distinguished from other causes in children 1, 3

Drug-Induced Causes

• Drug hypersensitivity reactions can cause petechial rash on palms and soles 1, 2

Mechanical and Traumatic Causes

• Increased capillary pressure from trauma, intense vomiting, or coughing can cause localized petechiae 2, 6
• Tourniquet phenomenon in well-appearing infants (e.g., from diapers or clothing) typically causes localized petechiae to lower limbs, often bilateral 7
• Negative pressure combined with muscular action (e.g., from fellatio) can cause soft palate petechiae 8

Other Systemic Causes

• Disseminated gonococcal infection, Mycoplasma pneumoniae, and leptospirosis can cause petechial rash 1, 2
• Hematologic malignancies such as T-cell acute lymphoblastic lymphoma-leukemia can present with petechial rash and require bone marrow assessment 9

Critical Diagnostic Approach

Immediate Assessment Required When:

• Fever with petechiae (consider meningococcemia or RMSF) 1
• Systemic symptoms: severe headache, altered mental status, hypotension 1
• Rapidly progressive rash 1
• Petechiae involving palms and soles 1, 2

Laboratory Evaluation:

• Complete blood count with platelet count for all patients with unexplained petechiae 1, 3
• PT, aPTT, and fibrinogen if bleeding disorder suspected 1
• Blood cultures if febrile or systemically ill 1
• Consider specialized testing (von Willebrand studies, platelet function testing) if initial screening normal but clinical suspicion high 1

Observation Strategy for Well-Appearing Infants:

• Localized petechiae without fever in well-appearing infants may warrant 4-hour observation period rather than extensive testing 7
• If no progression of signs, likely benign mechanical cause 7