Aesthetic Dermatology MCQ - Trichloroacetic acid

A 45-year-old woman with Fitzpatrick skin type II presents with moderate photodamage, fine perioral rhytides, and mottled hyperpigmentation. She has no history of keloids or herpes simplex virus and is seeking a medium-depth chemical peel. Which of the following agents is most appropriate for achieving controlled epidermal and papillary dermal injury with minimal risk of hypopigmentation in this patient?

A) 35% trichloroacetic acid (TCA)
B) 88% phenol
C) 50% glycolic acid
D) Jessner's solution
E) Salicylic acid 30%

Correct Answer: A) 35% trichloroacetic acid (TCA)

Explanation

Chemical peels are classified by their depth of penetration: superficial, medium, or deep. This patient is a candidate for a medium-depth peel to address photodamage and rhytides.

Why 35% TCA is the Best Choice:

• Depth of Penetration: 35% TCA typically penetrates to the papillary dermis, making it a classic medium-depth peeling agent. It effectively improves photodamage, fine rhytides, and hyperpigmentation.

• Safety Profile: In Fitzpatrick skin type II, the risk of hypopigmentation is low with TCA, unlike with deeper peels (e.g., phenol). TCA does not cause systemic toxicity.

• Controlled Application: The frost response (white frosting due to protein coagulation) allows for precise monitoring of peel depth.

• Histologic Effects: Causes epidermolysis and collagen coagulation in the papillary dermis, stimulating neocollagenesis.

Why Not the Other Options?

• (B) 88% phenol: A deep peeling agent that penetrates to the reticular dermis. It is highly effective for severe rhytides but carries a significant risk of hypopigmentation (permanent bleaching), cardiotoxicity, and scarring. It is not appropriate for this patient's moderate concerns.

• (C) 50% glycolic acid: A superficial peeling agent that targets the epidermis. It is good for mild dyspigmentation but insufficient for moderate rhytides or dermal remodeling.

• (D) Jessner's solution: A superficial peel (resorcinol, salicylic acid, lactic acid in ethanol) that causes epidermolysis. It is used for acne, melasma, and mild photodamage but does not reach the papillary dermis.

• (E) Salicylic acid 30%: A superficial peel that is comedolytic and anti-inflammatory. It is excellent for acne but not for rhytides or significant photodamage.

Preoperative Considerations:

• Priming: Pre-treatment with retinoids (e.g., tretinoin) for 4-6 weeks to enhance peel penetration and uniformity.

• HSV Prophylaxis: Although no history, consider prophylactic antivirals due to risk of reactivation.

• Sun Protection: Crucial to prevent post-inflammatory hyperpigmentation.

Postoperative Course:

• Healing: Re-epithelialization in 7-10 days with erythema that may persist for weeks.

• Results: Gradual improvement in texture and pigmentation over months.

Prognosis:
Excellent for moderate photodamage with proper technique. Deeper peels or combination therapy may be needed for severe damage.

Note: TCA 35% is the workhorse for medium-depth peels. The concentration can be adjusted (e.g., 20-30% for lighter peels, 40-50% for deeper effects) based on the patient's needs and skin type. Always test Fitzpatrick skin type and assess scarring tendency before proceeding.