Dermatology MCQ - Viral Infections - Dengue Fever

A 22-year-old traveler returns from Southeast Asia with a high fever, severe headache, retro-orbital pain, and myalgia. On examination, you note a diffuse macular rash and mild petechiae on the extremities. Tourniquet test is positive. Laboratory studies reveal leukopenia and thrombocytopenia. On day 4 of illness, the fever resolves, but the patient develops abdominal pain, vomiting, and restlessness. Which of the following is the most likely diagnosis and the critical pathophysiological process occurring at this stage?

A) Dengue fever; plasma leakage due to increased vascular permeability
B) Malaria; hemolytic anemia due to Plasmodium infection
C) Typhoid fever; gastrointestinal hemorrhage due to Salmonella typhi
D) Chikungunya; arthritis due to viral synovitis
E) Leptospirosis; hepatic and renal injury due to Leptospira

Correct Answer: A) Dengue fever; plasma leakage due to increased vascular permeability

Explanation

This presentation is classic for dengue fever, with progression to the critical phase around the time of defervescence.

Key Clinical Features of Dengue:

• Febrile Phase (Days 1-3): High fever, severe headache, retro-orbital pain, myalgia/arthralgia ("breakbone fever"), and a maculopapular rash. Positive tourniquet test, leukopenia, and thrombocytopenia are common.

• Critical Phase (Days 4-7): Occurs as fever resolves. Increased vascular permeability leads to plasma leakage, which can result in:

  • Abdominal pain, vomiting, pleural effusions, ascites.

  • Hemoconcentration (rising hematocrit).

  • Shock (dengue shock syndrome) if severe.

  • Hemorrhagic manifestations (petechiae, mucosal bleeding) due to thrombocytopenia and coagulopathy.

• Recovery Phase: Reabsorption of leaked plasma, often with a second rash ("isles of white in a sea of red").

Why This is Dengue:

• The biphasic pattern (fever resolution followed by worsening) is highly characteristic.

• Plasma leakage is the hallmark of severe dengue (formerly dengue hemorrhagic fever/dengue shock syndrome). It is mediated by cytokine activation and endothelial dysfunction.

• The tourniquet test is a bedside test for capillary fragility (≥20 petechiae per 2.5 cm² indicates positivity).

Why Not the Other Options?

• (B) Malaria: Causes fever, hemolytic anemia, and thrombocytopenia but does not have a distinct critical phase with plasma leakage. Headache and myalgia are less prominent.

• (C) Typhoid fever: Causes fever, abdominal pain, and rose spots (not a diffuse rash), but no plasma leakage or thrombocytopenia.

• (D) Chikungunya: Causes fever, rash, and severe arthralgia/arthritis, but no plasma leakage or shock.

• (E) Leptospirosis: Causes fever, jaundice, and renal injury, but no characteristic biphasic pattern or plasma leakage.

Management:

• Supportive care: Aggressive fluid resuscitation with isotonic crystalloids during the critical phase. Monitor hematocrit and vital signs closely.

• Avoid: NSAIDs (increase bleeding risk) and overhydration (can cause pulmonary edema).

• Prevention: Mosquito control and vaccine (Dengvaxia® in seropositive individuals only).

Prognosis:
Most cases are self-limiting, but severe dengue has a mortality of <1% with proper fluid management.

Note: Dengue is caused by four serotypes (DENV 1-4). Secondary infection with a different serotype increases the risk of severe disease due to antibody-dependent enhancement (ADE). Always consider dengue in febrile travelers from endemic areas.