Dermatology MCQ - Inflammatory Dermatoses - Infective dermatitis

A 9-year-old child from a tropical region presents with a severe, chronic, exudative, and crusted dermatitis affecting the scalp, ears, and perinasal and perioral areas. The child has associated generalized lymphadenopathy. The eruption has been present for years and is only partially responsive to antibiotic courses and topical corticosteroids. Which of the following is the most specific investigation to confirm the underlying diagnosis?

A. Bacterial culture from the exudate
B. Serological test for HTLV-1 antibody
C. KOH preparation of skin scrapings
D. Patch testing for allergic contact dermatitis
E. Measurement of serum IgE levels

Correct Answer: B. Serological test for HTLV-1 antibody

Explanation:

• The presentation is highly characteristic of Infective Dermatitis associated with HTLV-1 (IDH). This is a severe, chronic, and recurrent eczematous condition seen almost exclusively in children who are carriers of the Human T-cell Lymphotropic Virus Type 1 (HTLV-1). The classic features include its chronicity, specific distribution (scalp, retroauricular areas, perinasal, perioral, and other intertriginous sites), a characteristic "weeping" and crusted appearance, and associated generalized lymphadenopathy. It is notoriously difficult to treat and serves as a marker for a significantly increased risk of future adult T-cell leukemia/lymphoma (ATLL).

• Why the other options are incorrect:

  • A. Bacterial culture from the exudate: While this would likely grow Staphylococcus aureus or Streptococcus pyogenes due to secondary impetiginization, this is a consequence of the condition, not the cause. The dermatitis recurs despite repeated antibiotic treatment.

  • C. KOH preparation of skin scrapings: This is used to diagnose dermatophyte (fungal) infections. The distribution and morphology described are not typical of tinea.

  • D. Patch testing for allergic contact dermatitis: This is used to identify type IV hypersensitivity. The early childhood onset, specific distribution, and systemic findings (lymphadenopathy) point away from a simple contact allergy.

  • E. Measurement of serum IgE levels: While levels may be elevated, this is a non-specific finding seen in many atopic and non-atopic conditions. It does not confirm the diagnosis of HTLV-1-associated infective dermatitis.

Key Points for Exams

• Pathogenesis: IDH is considered a direct manifestation of HTLV-1 infection in children. The virus disrupts immune regulation, leading to chronic skin inflammation and profound susceptibility to bacterial superinfection.

• Epidemiology: Strongly associated with geographic regions where HTLV-1 is endemic, including the Caribbean, southwestern Japan, parts of Central Africa, and South America.

• Major Complication: Children with IDH are at a markedly increased risk of developing Adult T-cell Leukemia/Lymphoma (ATLL) later in life. Therefore, it is a crucial diagnostic marker.

• Prognosis: The dermatitis itself is chronic and relapsing. The long-term prognosis is guarded due to the associated risk of ATLL.

• Management:

  1. Long-term Antibiotics: Prolonged courses of antibiotics (e.g., sulfamethoxazole-trimethoprim) are used to control the chronic bacterial superinfection and can help suppress the dermatitis.

  2. Topical Therapy: Topical corticosteroids and emollients are used to manage the inflammatory component.

  3. Supportive Care: Meticulous skin hygiene is essential.

  4. Monitoring: These patients require long-term hematologic follow-up for early detection of ATLL.