Dermatology MCQ - Viral Infections - Gianotti–Crosti syndrome

A 2-year-old child presents with a symmetric, non-pruritic eruption of monomorphic, flat-topped, pink-brown papules on the cheeks, extensor surfaces of the extremities, and buttocks. The child has no fever but has mild hepatomegaly. The mother reports the child had an upper respiratory infection several weeks prior. Which of the following is the most likely diagnosis and its most common viral trigger?

A) Gianotti-Crosti syndrome; hepatitis B virus
B) Papular acrodermatitis of childhood; Epstein-Barr virus
C) Molluscum contagiosum; poxvirus
D) Hand, foot, and mouth disease; coxsackievirus A16
E) Erythema infectiosum; parvovirus B19

Correct Answer: A) Gianotti-Crosti syndrome; hepatitis B virus

Explanation

This presentation is classic for Gianotti-Crosti syndrome (GCS), also known as papular acrodermatitis of childhood.

Key Clinical Features of Gianotti-Crosti Syndrome:

• Exanthem: Symmetrical, monomorphic, flat-topped, firm, pink to flesh-colored papules (1-5 mm in diameter).

• Distribution: Predilection for the face (cheeks), extensor surfaces of the extremities (elbows, knees), and buttocks. The trunk is often spared.

• Symptoms: Typically non-pruritic (though pruritus can occur), and the child is usually afebrile and well-appearing.

• Systemic Findings: Hepatomegaly and mild lymphadenopathy may be present. Acute anicteric hepatitis is common.

• Course: The eruption persists for 2-4 weeks and resolves spontaneously without sequelae.

Virologic Associations:

• Most Common Trigger: Hepatitis B virus (particularly genotype D) was the original trigger described. However, in many regions, other viruses are now more common due to HBV vaccination.

• Other Common Triggers: Epstein-Barr virus, cytomegalovirus, enteroviruses, parvovirus B19, and respiratory syncytial virus.

• Pathogenesis: Believed to be a cutaneous immune response to viral antigens.

Why Not the Other Options?

• (B) Papular acrodermatitis of childhood: This is a synonym for Gianotti-Crosti syndrome. While Epstein-Barr virus can trigger it, hepatitis B virus is the classic and most historically significant association.

• (C) Molluscum contagiosum: Presents as umbilicated, pearly papules, not flat-topped monomorphic papules. It is not associated with hepatomegaly.

• (D) Hand, foot, and mouth disease: Causes vesicles and erosions on the hands, feet, and oral mucosa, not monomorphic papules on the face and extremities.

• (E) Erythema infectiosum: Presents with a "slapped cheek" rash and a lacy reticular exanthem on the body, not monomorphic papules on the extremities and buttocks.

Management:

• Supportive care: Reassurance, as the condition is self-limiting.

• Investigation: Serologic testing for hepatitis B virus and other potential triggers (e.g., EBV, CMV) may be considered, especially if hepatomegaly or abnormal LFTs are present.

• No specific treatment is required for the rash.

Prognosis:
Excellent; the rash resolves without scarring. The associated hepatitis is typically anicteric and resolves spontaneously.

Note: Gianotti-Crosti syndrome is a distinct viral exanthem. The classic description is "monomorphic papules on the face, extremities, and buttocks with hepatitis." While HBV was the prototypic trigger, always consider other viral etiologies based on epidemiology and vaccination status.