## Clinical Diagnosis: Dengue Fever with Warning Signs ### Key Clinical Features **Key Point:** The constellation of high fever, retro-orbital pain, myalgias, thrombocytopenia (85,000/μL), and haemoconcentration (Hct 48%) with a positive tourniquet test is pathognomonic for dengue fever in the febrile phase. ### Diagnostic Criteria | Feature | Dengue | Chikungunya | Zika | |---------|--------|-------------|------| | **Fever duration** | 3–7 days | 3–7 days | 2–7 days | | **Retro-orbital pain** | ✓ (classic) | ✗ (rare) | ✗ | | **Myalgias** | ✓ (moderate) | ✓✓ (severe, incapacitating) | ✗ (mild) | | **Arthralgia** | ✗ | ✓✓ (prominent) | ✓ (mild) | | **Thrombocytopenia** | ✓ (common) | ✗ (rare) | ✗ | | **Haemoconcentration** | ✓ | ✗ | ✗ | | **Rash timing** | Day 3–4 (after fever) | Day 1–2 | Day 3–4 | ### Dengue Severity Classification **High-Yield:** This patient has **warning signs** (platelet count <100,000/μL + haemoconcentration) but no severe dengue features (shock, bleeding, organ dysfunction). She requires close monitoring for progression to dengue haemorrhagic fever (DHF). ### Pathophysiology 1. Viraemia peaks during febrile phase (days 1–5) 2. Platelet destruction via antibody-dependent cellular cytotoxicity (ADCC) 3. Vascular permeability increases → haemoconcentration 4. Tourniquet test positive due to capillary fragility **Clinical Pearl:** Retro-orbital pain is so characteristic of dengue that its absence should prompt consideration of alternative diagnoses. ### Management Implications - Supportive care with IV fluids if warning signs present - Daily platelet and haematocrit monitoring - Avoid NSAIDs (bleeding risk); use paracetamol - Watch for critical phase (days 5–7) when fever defervesces [cite:Park 26e Ch 5]
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