Model Answer
0 min readIntroduction
A complete diagnosis requires a thorough clinical assessment, including patient history, physical examination, and relevant investigations. In the absence of a specific case presentation, we will construct a scenario: a 5-year-old male child presents with a 3-day history of fever (maximum 102°F), followed by a maculopapular rash that started on the trunk and spread to the face and limbs. The child is otherwise playful, eating normally, but appears mildly fatigued. This presentation necessitates a differential diagnosis encompassing common infectious exanthems and other potential causes.
Differential Diagnosis
Based on the initial presentation of fever followed by a rash, the following differential diagnoses must be considered:
- Measles (Rubeola): Characterized by a prodrome of fever, cough, coryza, and conjunctivitis, followed by a maculopapular rash starting on the face and spreading downwards. Koplik spots (small white spots on the buccal mucosa) are pathognomonic.
- Rubella (German Measles): Similar to measles but milder. Rash is typically maculopapular, starting on the face and spreading rapidly. Lymphadenopathy, particularly postauricular and occipital, is common.
- Varicella (Chickenpox): Presents with a vesicular rash in different stages of development (papules, vesicles, pustules, crusts). The rash is typically pruritic.
- Roseola Infantum (Exanthem Subitum): Characterized by a high fever for 3-5 days, followed by a sudden defervescence and the appearance of a maculopapular rash.
- Scarlet Fever: Associated with a streptococcal pharyngitis. Rash is fine, red, and sandpaper-like, often starting in the neck and axillae. Strawberry tongue is a characteristic finding.
- Drug Eruption: Considered if the child has recently started any new medications.
- Kawasaki Disease: Though less common, it should be considered, especially if there are other suggestive features like conjunctivitis, changes in the oral mucosa, lymphadenopathy, and extremity changes.
Investigations
To narrow down the differential diagnosis, the following investigations are crucial:
- Complete Blood Count (CBC): To assess for leukocytosis or lymphocytosis, which can suggest viral or bacterial infection.
- Viral Serology:
- Measles IgM and IgG
- Rubella IgM and IgG
- Varicella-Zoster Virus (VZV) PCR or antibody testing
- Streptococcal Antigen Rapid Test (or Throat Culture): To rule out streptococcal pharyngitis and scarlet fever.
- Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP): To assess for inflammation, particularly if Kawasaki disease is suspected.
- Liver Function Tests (LFTs): To evaluate liver involvement, which can occur in some viral infections.
Final Diagnosis & Justification
Let's assume the following investigation results are obtained:
- CBC: Normal white blood cell count with a slight increase in lymphocytes.
- Measles IgM: Negative
- Rubella IgM: Positive
- VZV PCR: Negative
- Streptococcal Antigen Rapid Test: Negative
- ESR and CRP: Normal
Based on the clinical presentation (fever followed by maculopapular rash) and the positive Rubella IgM, the most likely diagnosis is Rubella (German Measles). The negative measles IgM rules out measles. The negative VZV PCR excludes chickenpox. The absence of streptococcal infection excludes scarlet fever. The normal ESR and CRP make Kawasaki disease less likely, although it cannot be entirely excluded without further evaluation if atypical features are present.
Management
Management of Rubella is primarily supportive, including rest, fluids, and antipyretics for fever. Pregnant women exposed to Rubella are at risk of congenital Rubella syndrome and require specific counseling and monitoring. Vaccination against Rubella (MMR vaccine) is the most effective preventative measure.
Conclusion
In conclusion, a systematic approach to diagnosis, starting with a thorough history and physical examination, followed by targeted investigations, is crucial in pediatric cases presenting with fever and rash. In this constructed scenario, the clinical and laboratory findings strongly suggest a diagnosis of Rubella. Early and accurate diagnosis allows for appropriate management and prevention of complications, as well as public health measures to control the spread of infection.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.