Diagnosis: Immune Thrombocytopenic Purpura (ITP) — Acute Childhood Form

Why this diagnosis fits

Pathophysiology

Clinical Features of Childhood ITP

• Sudden onset of petechiae or purpura, days to weeks after a viral illness
• Child appears well (no fever, not toxic)
• No lymphadenopathy, no hepatosplenomegaly (if present, consider leukemia or other causes)
• Bleeding correlates with platelet count:

  • 50,000/mm³ → incidental finding

  • 30,000–50,000/mm³ → easy bruising
  • 10,000–30,000/mm³ → spontaneous petechiae/ecchymoses
  • <10,000/mm³ → risk of internal/intracranial bleeding

Diagnosis

• CBC: isolated thrombocytopenia (normal WBC, Hb)
• Peripheral blood smear: large, immature platelets (megathrombocytes); no blasts, no schistocytes
• Exclude: SLE, HIV, hepatitis C, lymphoproliferative disorders, drug-induced thrombocytopenia
• Bone marrow biopsy is not routinely required in typical childhood ITP

Management

1. Observation alone — many childhood ITP cases resolve spontaneously within weeks to months (>80% resolve within 6 months)
2. Oral prednisone 1.0–1.5 mg/kg/day — first-line if treatment is needed
3. IV immunoglobulin (IVIG) — rapid platelet rise, used when faster response needed
4. Anti-D immunoglobulin — in Rh-positive, non-splenectomized patients
5. Splenectomy — reserved for chronic ITP (>12 months) refractory to medical therapy; avoided in young children if possible

A rapid response to steroids is consistent with ITP. A poor response to steroids but good response to platelet transfusion suggests an inherited thrombocytopenia syndrome instead.

Key Distinguishing Points (Childhood vs Adult ITP)

Differential Diagnosis: Petechial Rash in a Well-Appearing 5-Year-Old, Post-Viral, No Organomegaly

1. Most Likely — ITP (as already discussed)

2. Other Causes of Thrombocytopenic Purpura (Low Platelets)

Acute Leukemia (ALL — most important to exclude)

• Most common childhood malignancy
• Key distinguishing features that argue AGAINST it in this case:
  • Leukemia typically causes organomegaly (hepatosplenomegaly, lymphadenopathy)
  • Child is usually sick-looking, pallid, fatigued
  • CBC shows pancytopenia (anemia + neutropenia + thrombocytopenia), not isolated thrombocytopenia
  • Blasts on peripheral smear
• A bone marrow biopsy differentiates if doubt remains

Aplastic Anemia

• Bone marrow failure → pancytopenia
• Child appears unwell, pallid, prone to infections
• No organomegaly (unlike leukemia)
• Peripheral smear: hypocellular marrow on biopsy; no blasts
• Argues against: isolated thrombocytopenia, post-viral, well child

Drug-Induced Thrombocytopenia

• Certain antibiotics (penicillins, sulfonamides), NSAIDs, anticonvulsants, valproate
• History of recent drug exposure is key
• Normal bone marrow megakaryocytes; resolves on stopping drug

Viral-Induced Thrombocytopenia (Direct Marrow Suppression)

• EBV, CMV, parvovirus B19, HIV, rubella, varicella can directly suppress platelet production
• Usually transient
• Can be difficult to distinguish from post-viral ITP; serology helps
• Parvovirus B19 specifically noted to cause transient thrombocytopenia and even ITP-like picture

Wiskott-Aldrich Syndrome

• X-linked; affects boys
• Triad: thrombocytopenia (small platelets), eczema, recurrent infections (immunodeficiency)
• Presents in infancy, not typically at age 5 without prior diagnosis
• Small platelets on smear (vs. large in ITP)

Thrombocytopenia with Absent Radii (TAR Syndrome)

• Congenital; usually diagnosed in neonatal period
• Absent radii bilaterally with thrombocytopenia
• Not a new presentation at age 5

3. Non-Thrombocytopenic Purpura (Normal Platelet Count)

Henoch-Schönlein Purpura (HSP) / IgA Vasculitis ⭐

• Most common vasculitis in children
• Palpable purpura (raised, not flat), typically over buttocks and lower limbs (gravity-dependent)
• Associated with: arthralgia/arthritis, colicky abdominal pain, renal involvement (haematuria)
• Normal platelet count — this is a leukocytoclastic vasculitis, not thrombocytopenia
• Often post-viral or post-streptococcal
• Differs from ITP: distribution of rash (buttocks/legs), palpable lesions, joint/GI symptoms

Meningococcal Septicaemia (Neisseria meningitidis) ⭐⭐ MUST NOT MISS

• Medical emergency — even though child appears well initially, this can deteriorate rapidly
• Petechiae may be the first sign, rapidly progressing to non-blanching purpura
• Key features: fever, irritability, rapidly spreading rash, blanching initially then non-blanching
• Child is usually sick — but early disease can appear deceptively well
• This must be actively excluded in any child with petechiae — do not discharge without ruling out

Rocky Mountain Spotted Fever / Rickettsial illness

• Tick exposure history
• Fever, headache, rash spreading centripetally (wrists/ankles → trunk)
• DIC can develop

Vasculitis (other causes)

• SLE — rare at age 5, but can present with thrombocytopenia + rash
• Anti-nuclear antibodies, complement levels help

4. Platelet Function Disorders (Normal Count, Abnormal Function)

• Glanzmann Thrombasthenia — normal count, absent platelet aggregation; mucocutaneous bleeding
• Bernard-Soulier Syndrome — large platelets, mild thrombocytopenia, von Willebrand receptor defect
• These present from infancy; post-viral trigger would not be typical

Summary Table

Clinical Approach to Exclude Differentials

1. CBC with differential — isolated thrombocytopenia favours ITP; pancytopenia raises alarm
2. Peripheral blood smear — large platelets (ITP), blasts (leukaemia), small platelets (Wiskott-Aldrich)
3. Press-blanch test — non-blanching confirms petechiae/purpura; blanching = macular erythema
4. Vital signs + clinical reassessment — exclude meningococcaemia
5. Coagulation screen (PT, APTT) — normal in ITP; abnormal in DIC
6. Viral serology — EBV, CMV, parvovirus B19
7. Bone marrow biopsy — only if atypical features (organomegaly, pancytopenia, failure to respond to treatment)