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Petechial rash

Medicine > Infection

Differential Diagnosis Schema 🧠

Infectious Causes

  • Meningococcaemia: Rapidly spreading petechial rash, fever, headache, neck stiffness; often associated with meningitis and septicaemia.
  • Endocarditis: Petechiae on the skin, mucous membranes, or conjunctiva; associated with fever, heart murmurs, and splinter haemorrhages.
  • Rocky Mountain spotted fever: Tick-borne illness with petechial rash starting on wrists and ankles, fever, and myalgia.
  • Sepsis: Petechiae due to disseminated intravascular coagulation (DIC); associated with hypotension, fever, and multi-organ failure.
  • Viral infections (e.g., dengue, enterovirus): Petechial rash with associated systemic symptoms like fever, arthralgia, and myalgia.
  • Scarlet fever: Fine red rash, which can include petechiae, particularly in skin folds; associated with sore throat and fever.
  • Infective mononucleosis: Petechial rash, especially after amoxicillin administration; associated with fever, sore throat, and lymphadenopathy.

Hematological Causes

  • Thrombocytopenia: Reduced platelet count leading to petechiae; causes include ITP, leukaemia, aplastic anaemia, and DIC.
  • Leukaemia: Bone marrow infiltration leading to pancytopenia, petechiae, and easy bruising; often accompanied by fatigue, pallor, and infections.
  • Aplastic anaemia: Pancytopenia with petechiae, fatigue, and increased susceptibility to infections; may be idiopathic or drug-induced.
  • Haemolytic uraemic syndrome (HUS): Triad of haemolytic anaemia, thrombocytopenia, and acute kidney injury; often preceded by a diarrhoeal illness.
  • Thrombotic thrombocytopenic purpura (TTP): Thrombocytopenia, haemolytic anaemia, neurological symptoms, renal impairment, and fever.
  • Disseminated intravascular coagulation (DIC): Widespread activation of clotting cascade causing petechiae, bleeding, and thrombosis; associated with sepsis, trauma, and malignancy.
  • Scurvy: Vitamin C deficiency causing impaired collagen synthesis, leading to petechiae, gingival bleeding, and poor wound healing.
  • Drug-induced thrombocytopenia: Common drugs include heparin, quinine, and some antibiotics; presents with petechiae and bleeding.
  • Liver disease: Impaired clotting factor production leading to petechiae and easy bruising; associated with jaundice and hepatomegaly.
  • Vitamin K deficiency: Leads to impaired synthesis of clotting factors, causing petechiae and bleeding; common in malabsorption or warfarin therapy.

Vasculitic and Autoimmune Causes

  • Henoch-Schönlein purpura (HSP): Palpable purpura typically on lower extremities, arthralgia, abdominal pain, and renal involvement.
  • Systemic lupus erythematosus (SLE): Autoimmune disorder with petechiae, malar rash, photosensitivity, and systemic involvement including renal and neurological.
  • Vasculitis (e.g., small vessel vasculitis): Presents with palpable purpura, systemic symptoms, and organ involvement depending on the type of vasculitis.
  • Rheumatoid arthritis: Can be associated with vasculitis causing petechiae, nodules, and systemic symptoms like joint pain and stiffness.
  • Behçet’s disease: Recurrent oral and genital ulcers, uveitis, and vasculitic rash including petechiae.
  • Cryoglobulinemia: Associated with hepatitis C infection; presents with petechiae, palpable purpura, arthralgia, and renal involvement.
  • Polyarteritis nodosa: Medium-vessel vasculitis with systemic symptoms, including petechiae, abdominal pain, and renal involvement.
  • Dermatomyositis: Autoimmune condition with heliotrope rash, Gottron’s papules, muscle weakness, and sometimes petechiae.
  • Goodpasture syndrome: Pulmonary-renal syndrome with haemoptysis, renal failure, and sometimes petechiae due to renal involvement.

Other Causes

  • Trauma or pressure: Petechiae can result from physical trauma, tight clothing, or prolonged pressure (e.g., from blood pressure cuff).
  • Coughing or vomiting: Severe coughing or vomiting can cause petechiae, particularly around the eyes or on the face.
  • Strenuous exercise: Intense physical exertion can lead to petechiae, often seen in weightlifters or runners.
  • Aging skin: Elderly patients may develop petechiae due to fragile blood vessels and thinning skin.
  • Platelet dysfunction: Conditions like Glanzmann’s thrombasthenia or drugs like aspirin can cause petechiae due to impaired platelet function.
  • Ehlers-Danlos syndrome: A connective tissue disorder leading to skin fragility and easy bruising, including petechiae.
  • Hypersensitivity vasculitis: Drug-induced small vessel vasculitis presenting with petechiae and systemic symptoms.
  • Malnutrition: Protein-calorie malnutrition can lead to skin changes including petechiae.
  • Radiation therapy: Can cause skin changes including petechiae, particularly in the irradiated field.

Key Points in History 🥼

Onset and Duration

  • Acute onset: Suggests infection, DIC, or drug reaction; consider meningococcaemia or sepsis in rapidly spreading petechiae.
  • Chronic or recurrent: More consistent with conditions like ITP, leukaemia, or autoimmune disorders such as SLE.
  • Intermittent symptoms: May indicate mild or chronic thrombocytopenia, vasculitis, or hypersensitivity reactions.
  • Recent trauma or pressure: History of physical trauma, tight clothing, or recent surgical procedures may explain localised petechiae.

Associated Symptoms

  • Fever and systemic symptoms: Suggests infection or systemic illness like sepsis, meningococcaemia, or viral infections.
  • Joint pain or swelling: Associated with vasculitis (e.g., HSP, SLE) or viral infections.
  • Bleeding or bruising: Easy bruising and mucosal bleeding suggest a haematological cause like thrombocytopenia or coagulopathy.
  • Weight loss and fatigue: Concerning for malignancy, particularly leukaemia or lymphoma.
  • Neurological symptoms: Headache, confusion, or focal neurological deficits may indicate DIC, TTP, or central nervous system vasculitis.
  • Abdominal pain: May be seen in HSP, vasculitis, or infectious causes like dengue fever.
  • Recent drug exposure: Consider drug-induced thrombocytopenia or hypersensitivity vasculitis.
  • Recent travel: Important for assessing risk of infections like dengue, malaria, or other tropical diseases.
  • Family history: Relevant for hereditary conditions like haemophilia, Ehlers-Danlos syndrome, or familial platelet disorders.
  • Previous similar episodes: History of recurrent petechiae could suggest chronic conditions like ITP or autoimmune diseases.

Background

  • Past medical history: Includes history of autoimmune disorders, haematological conditions, recent infections, or chronic illnesses.
  • Medication history: Review for drugs known to cause thrombocytopenia, coagulopathy, or hypersensitivity reactions.
  • Family history: Consider familial patterns of bleeding disorders, autoimmune diseases, or malignancies.
  • Social history: Includes recent travel, occupational exposures, and lifestyle factors like smoking or alcohol use.
  • Dietary history: Assess for potential deficiencies, such as vitamin C or K, that may contribute to petechiae.
  • Allergy history: Important if considering drug-induced hypersensitivity vasculitis or anaphylactic reactions.
  • Immunisation history: Consider in differential diagnoses involving infectious causes, especially in children.
  • Recent infections: Viral or bacterial infections can predispose to conditions like ITP, HSP, or septicaemia.
  • Occupational history: Relevant for exposures to chemicals or infections that may lead to haematological or systemic illness.
  • Recent procedures or surgeries: Important for assessing the risk of post-surgical thrombocytopenia, coagulopathy, or DIC.

Possible Investigations 🌡️

Laboratory Tests

  • Full blood count (FBC): To assess for thrombocytopenia, anaemia, or leukocytosis, which can suggest haematological or infectious causes.
  • Coagulation profile (PT, APTT, INR): To evaluate for coagulopathies, DIC, or liver dysfunction.
  • Blood cultures: Indicated if sepsis or endocarditis is suspected.
  • Liver function tests: To assess for hepatic causes of coagulopathy, including liver cirrhosis or hepatitis.
  • Renal function tests (U&E): To evaluate renal involvement in conditions like HUS, TTP, or vasculitis.
  • Peripheral blood smear: To assess for haematological abnormalities such as schistocytes in DIC or TTP, or blasts in leukaemia.
  • Inflammatory markers (CRP, ESR): Elevated in infections, vasculitis, or autoimmune diseases.
  • Autoantibody screen (ANA, ANCA): To assess for autoimmune conditions like SLE, vasculitis, or rheumatoid arthritis.
  • D-dimer: Elevated in DIC, thromboembolism, or severe sepsis.
  • HIV test: To assess for underlying immunodeficiency or associated conditions like thrombocytopenia.
  • Bone marrow biopsy: Considered in cases of unexplained thrombocytopenia or pancytopenia, or when leukaemia is suspected.
  • Urinalysis: To check for haematuria or proteinuria, which may indicate renal involvement in vasculitis or HSP.
  • Viral serology: For detecting viral causes such as dengue, CMV, or EBV infections.
  • Vitamin levels: Assess vitamin C (for scurvy) and vitamin K (for coagulopathy).
  • Immunoglobulin levels: May be useful in cases of recurrent infections or suspected immunodeficiency.

Imaging and Other Tests

  • Chest X-ray: To assess for pulmonary involvement in conditions like SLE, vasculitis, or Goodpasture syndrome.
  • Echocardiogram: Indicated if endocarditis or cardiac involvement in vasculitis is suspected.
  • Abdominal ultrasound: Useful in assessing abdominal organ involvement, especially in HSP or vasculitis.
  • CT/MRI: Consider for detailed imaging in cases of systemic illness, suspected malignancy, or organ involvement.
  • Skin biopsy: To confirm vasculitis or to rule out other causes of petechial rash such as malignancy or infection.
  • Lumbar puncture: Consider in cases of suspected meningitis or CNS vasculitis.
  • Electrocardiogram (ECG): To assess for arrhythmias or cardiac complications in systemic diseases.
  • Capillaroscopy: Can be used to assess microvascular changes in connective tissue diseases like SLE.

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