10.1 Acne & Psoriasis
Key Takeaways
- Acne vulgaris is graded as mild, moderate, or severe based on the quantity and type of lesions (comedones vs. inflammatory papules/pustules vs. nodulocystic lesions).
- Topical retinoids are the cornerstone of acne maintenance therapy, while oral isotretinoin is reserved for severe, nodulocystic, or refractory acne due to its profile of severe adverse effects and teratogenicity.
- To prevent bacterial resistance, topical or oral antibiotics used for inflammatory acne must always be co-prescribed with benzoyl peroxide, and systemic antibiotic courses should be limited to 3-4 months.
- Plaque psoriasis classically presents as well-demarcated erythematous plaques with silvery-white scales on extensor surfaces (knees, elbows) showing the Auspitz sign and Koebner phenomenon.
- Localized plaque psoriasis is primarily managed with high-potency topical corticosteroids, often combined with vitamin D analogues (calcipotriene) to increase efficacy and reduce steroid-induced skin atrophy.
1. Acne Vulgaris: Pathogenesis & Severity Grading
Acne vulgaris is a chronic inflammatory disorder of the pilosebaceous unit. Its pathogenesis is multifactorial and involves four primary interrelated processes: follicular hyperkeratinization (leading to microcomedone formation and follicular obstruction), androgen-induced excess sebum production from hyperactive sebaceous glands, follicular colonization by Cutibacterium acnes (an anaerobic diphtheroid bacterium that thrives in the lipid-rich sebum), and host-mediated inflammatory immune responses. Clinical severity grading is essential to guide step-up pharmacotherapy, as it distinguishes between non-inflammatory and inflammatory lesions:
- Mild Acne: Dominated by non-inflammatory comedones (open comedones or blackheads, and closed comedones or whiteheads) with very few, scattered inflammatory papules or pustules. Crucially, there are no deep nodulocystic lesions or scarring present.
- Moderate Acne: Characterized by a significant number of inflammatory papules and pustules on the face, chest, or back, with occasional painful nodules. Mild scarring may begin to appear if lesions are manipulated.
- Severe Acne: Defined by widespread, confluent inflammatory papules, pustules, and multiple deep, painful nodulocystic lesions or cysts, frequently accompanied by prominent scarring and sinus tracts.
| Severity Grade | Primary Lesions | First-Line Treatment Options |
|---|---|---|
| Mild | Comedones, sparse papules | Topical retinoid OR Benzoyl peroxide (BPO) OR Topical retinoid + BPO fixed-dose combination |
| Moderate | Many papules, pustules, few nodules | Topical combination (BPO + retinoid +/- topical antibiotic) OR Oral tetracycline antibiotic + topical retinoid + BPO |
| Severe | Multiple nodules, cysts, scarring | Oral Isotretinoin monotherapy OR Oral antibiotic + topical retinoid + BPO |
2. Topical Treatments for Acne Vulgaris: Mechanisms and Application
Topical agents target specific pathogenic pathways and form the foundation of mild-to-moderate acne therapy:
- Topical Retinoids (e.g., Tretinoin, Adapalene, Tazarotene): These vitamin A derivatives bind to nuclear retinoic acid receptors (RARs) to normalize follicular keratinocyte differentiation, reducing cohesion between epidermal cells and preventing microcomedone formation. They are the absolute cornerstone of both active acne clearing and long-term maintenance. Patients should apply a pea-sized amount to the entire face at night (not spot-treat). Principal adverse effects include localized erythema, dryness, peeling, and photosensitivity. Adapalene is the most stable and least irritating molecule, while tazarotene is highly potent but highly irritating.
- Benzoyl Peroxide (BPO): A powerful bactericidal agent that releases free oxygen radicals within the sebaceous follicle, rapidly destroying anaerobic C. acnes. Importantly, because of its physical mechanism of action, BPO does not induce bacterial resistance. Thus, BPO must always be co-prescribed whenever topical or oral antibiotics are used. Common side effects include skin irritation, contact dermatitis, and bleaching of clothing or hair.
- Topical Antibiotics (e.g., Clindamycin 1%, Erythromycin): These reduce C. acnes populations and suppress bacterial-induced inflammation. They must never be used as monotherapy due to the rapid selection of resistant strains; they are formulated in combination with BPO (e.g., clindamycin/benzoyl peroxide gel).
3. Systemic Treatments for Acne Vulgaris: Guidelines & Safety
Systemic therapies are indicated for moderate-to-severe inflammatory acne, cases with significant scarring potential, or when optimized topical regimens fail:
- Oral Antibiotics: Tetracyclines, specifically Doxycycline (100 mg daily or twice daily) or Minocycline, are preferred first-line systemic agents. They possess both antimicrobial properties against C. acnes and strong anti-inflammatory properties (via inhibition of matrix metalloproteinases and neutrophil chemotaxis). They are contraindicated during pregnancy (due to hepatotoxicity and fetal skeletal defects) and in children under 8 years of age (due to permanent teeth staining and bone growth deceleration). Use must be strictly capped at 3-4 months to prevent systemic resistance, and always combined with topical BPO. Doxycycline commonly causes gastrointestinal upset, photosensitivity, and drug-induced pill esophagitis (patients must take it with a full glass of water and remain upright for 30 minutes).
- Oral Isotretinoin: A highly effective oral retinoid indicated for severe nodulocystic acne, or moderate acne refractory to multiple courses of systemic antibiotics. It is the only treatment that targets all four pathogenic pathways of acne (dramatically reduces sebum size/output, normalizes keratinization, decreases C. acnes population, and reduces inflammation).
- Adverse Effects: Extremely teratogenic (causes craniofacial, cardiac, and CNS malformations), severe cheilitis, diffuse cutaneous and mucosal xerosis (dry skin, eyes, nosebleeds), hypertriglyceridemia, and elevated transaminases.
- Monitoring and iPLEDGE / UAE Regulations: Females of childbearing potential must utilize two highly effective forms of contraception, obtain two negative serum pregnancy tests prior to initiation, and undergo monthly pregnancy testing. Baseline and monthly serum lipids (triglycerides must be monitored; discontinue if triglycerides exceed 9 mmol/L or 800 mg/dL to prevent acute pancreatitis) and liver function tests (LFTs; discontinue if transaminases rise more than 3 times the upper limit of normal) are mandatory. A 1-month washout period is required after stopping the drug before pregnancy can be safely attempted.
- Hormonal Therapy: Spironolactone (an aldosterone antagonist with anti-androgen properties) or combined oral contraceptives containing low-dose estrogen and a low-androgenicity progestin (e.g., drospirenone) are effective second-line therapies for female patients, particularly those presenting with cyclic, jawline-distributed flares.
4. Plaque Psoriasis: Clinical Presentation and Pathophysiology
Psoriasis is a chronic, immune-mediated systemic inflammatory disease characterized by epidermal hyperplasia. Its pathogenesis is driven by a dendritic cell-mediated activation of helper T-cells (specifically the IL-23/IL-17 cytokine axis). This leads to massive keratinocyte hyperproliferation and an accelerated epidermal cell transit time: the normal epidermal cell cycle is compressed from 28 days down to just 3 to 5 days, resulting in immature keratinocytes accumulating on the skin surface. Chronic plaque psoriasis (psoriasis vulgaris) is the most common variant, presenting with:
- Lesions: Symmetrical, sharply demarcated, erythematous plaques covered by thick, adherent, silvery-white scales.
- Distribution: Classically localizes to extensor surfaces (knees, elbows), the scalp, the lumbosacral region, and the umbilicus.
- Auspitz Sign: The appearance of pinpoint bleeding when the silvery scale is gently scraped off. This occurs because the epidermal layer overlying the elongated dermal papillae is extremely thin, exposing dilated, tortuous capillaries underneath.
- Koebner Phenomenon: The development of new psoriate plaques at sites of physical trauma or skin injury (such as scratches, surgical incisions, or sunburns).
- Nail Psoriasis: Features fine nail pitting (due to parakeratosis of the nail matrix), distal onycholysis (separation of the nail plate from the bed), and "oil-drop" hyperpigmentation under the nail plate.
5. Topical Steroid Management and Systemic Referrals
For localized plaque psoriasis (involving less than 10% of the body surface area), topical management is the first-line standard:
- Topical Corticosteroids: Grouped by potency from Class I (superpotent, e.g., Clobetasol propionate 0.05% ointment) to Class VII (low potency, e.g., Hydrocortisone 1% cream).
- Regimen: Active, thick plaques on the trunk or limbs are cleared using Class I or II superpotent steroids twice daily for up to 2-4 weeks. Once cleared, patients transition to lower-potency maintenance or a weekend-only pulse regimen to prevent tachyphylaxis and local side effects. Low-potency steroids (Class VI/VII) should be used exclusively on the face and intertriginous folds (axilla, groin) because these areas have thin skin and absorb steroids rapidly.
- Side Effects: Skin atrophy (thinning), telangiectasias, striae, and hypothalamic-pituitary-adrenal (HPA) axis suppression. Limit superpotent steroid use to less than 50g per week to avoid systemic absorption.
- Vitamin D Analogues (Calcipotriene, Calcitriol): Inhibit keratinocyte proliferation and induce differentiation. They are frequently formulated as a fixed-dose combination with a Class II steroid (e.g., calcipotriene/betamethasone dipropionate) to achieve synergistic clearing while reducing the risk of steroid-induced skin atrophy.
- Calcineurin Inhibitors (e.g., Topical Tacrolimus 0.1%): Excellent steroid-sparing agents particularly suitable for the face, ears, and intertriginous areas where steroids are contraindicated for long-term use.
- Systemic Therapies & Referral: For moderate-to-severe disease (>10% body surface area), GPs must refer to dermatology. Systemic therapies include Methotrexate (oral/SC, weekly dosing, mandatory daily folic acid supplementation, monitored with baseline/periodic LFTs, CBC, and contraindicated in pregnancy due to teratogenicity) and biologics targeting TNF-alpha (Adalimumab), IL-17 (Secukinumab), or IL-23 (Ustekinumab). Biologics require mandatory screening for latent tuberculosis (via IGRA or PPD) and chronic hepatitis B/C before initiation.
A 16-year-old female presents with multiple closed and open comedones on her forehead and nose, with 3 inflammatory papules and no nodules or cysts. What is the most appropriate first-line therapy?
A 24-year-old male with severe nodulocystic acne is scheduled to begin oral isotretinoin. Which of the following parameters must be monitored at baseline and monthly during therapy?
A 35-year-old female presents with well-demarcated erythematous plaques covered by silvery-white scales on her bilateral elbows and knees. Pinpoint bleeding is noted when a scale is peeled off. Which of the following is the most appropriate initial treatment for these localized lesions?