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Acne in Clinical Practice: A PLAB 2 Candidate’s Guide


Acne is a high-yield topic for PLAB 2. Examiners expect you to know classification, management per NICE (NG198, 2021, reviewed 2023), drug mechanisms, contraindications, and differentiating mimics like rosacea. Here’s a structured overview.



🔹 Lesion Glossary (Know the Difference)

  • Comedones (hallmark of acne vulgaris): Blocked follicles.

    • Open (blackheads), Closed (whiteheads).

  • Papules: Small, raised, red, inflamed, no pus.

  • Pustules: Papules with central pus.

  • Nodules: Larger, firm, deep, tender inflammatory lesions.

  • Cysts: Fluctuant, pus-filled, often scarring.

👉 Key PLAB point: Comedones are seen only in acne vulgaris — not in rosacea or drug-induced eruptions.



🔹 Risk Factors for Acne Vulgaris


1. Physiological / Hormonal

  • Puberty → surge in androgens → ↑ sebaceous gland activity.

  • Androgen excess (e.g., PCOS, congenital adrenal hyperplasia, androgen-secreting tumours).

  • Menstrual cycle → premenstrual flare-ups.

  • Pregnancy (hormonal changes can worsen acne).


2. Genetic / Family History

  • Strong hereditary component.

  • Family history of severe acne or scarring increases risk.


3. Medications (Drug-induced acneiform eruptions)

  • Corticosteroids (“steroid acne”).

  • Lithium.

  • Phenytoin.

  • Isoniazid.

  • EGFR inhibitors (e.g., cetuximab).

  • Anabolic steroids.


4. Mechanical / Occupational Factors

  • Friction/pressure/occlusion → “Acne mechanica” (helmets, tight clothing, masks).

  • Occupational exposures → oils, hydrocarbons, tar, chlorine compounds (“chloracne”).


5. Cosmetic / Skin-care Related

  • Use of comedogenic cosmetics (“acne cosmetica”).

  • Heavy, oily moisturisers, sunscreens, or hair products.


6. Lifestyle / Diet (evidence mixed but recognised by NICE & journals)

  • High glycaemic index foods (spikes insulin/IGF-1 → sebum + keratinisation).

  • Dairy products (especially skimmed milk, possibly due to hormones).

  • Obesity / metabolic factors (hormonal interplay).

  • Stress (alters cortisol/androgen levels, worsens flares).

  • Smoking → associated with inflammatory and comedonal acne in some studies.


7. Contraception

  • Combined oral contraceptives (COCs) can improve acne.

  • ⚠️ Progestogen-only pill or implant can worsen acne (NICE/NHS).



🔹 Classification of Acne by Severity

  • Mild: Comedones ± few papules/pustules, little inflammation.

  • Moderate: More papules/pustules, mild inflammation, face ± trunk.

  • Moderate–severe: Numerous inflammatory lesions, widespread, few nodules, scarring risk.

  • Severe (nodulocystic/conglobata): Nodules, cysts, scarring, psychological impact.



🔹 NICE-Recommended Treatment Pathway

Mild Acne

  • Topical fixed combination: adapalene + benzoyl peroxide (preferred), OR tretinoin + clindamycin, OR BPO + clindamycin.

  • Alternative: Azelaic acid monotherapy.

Moderate Acne

  • Same topical combinations, OR oral lymecycline/doxycycline + topical agent.

Moderate–Severe Acne

  • Oral lymecycline/doxycycline + adapalene + BPO, OR oral antibiotic + azelaic acid.

  • ❗ Always combine oral antibiotic with a topical non-antibiotic to prevent resistance.

Severe Acne / Resistant Acne

  • Refer to dermatology.

  • Oral isotretinoin under specialist supervision.



🔹 Isotretinoin (Specialist-Only)

  • MOA: ↓ sebum, normalises keratinisation, ↓ C. acnes, anti-inflammatory.

  • Indications: Severe/resistant acne, scarring, or psychological impact.

  • Contraindications: Pregnancy, breastfeeding, severe liver disease, tetracycline co-use.

  • Adverse effects: Cheilitis, dry skin/eyes, teratogenicity, psychiatric effects, ↑ LFTs/lipids, musculoskeletal pain.

  • Monitoring: PPP, baseline + periodic LFTs/lipids, mood checks.



🔹 Role of Oral Tetracyclines

  • MOA: Antibacterial + anti-inflammatory.

  • Drugs: Lymecycline, doxycycline (better tolerated than minocycline).

  • Course: 12 weeks, max 6 months.

  • Always with topical non-antibiotic (e.g., BPO/retinoid).



🔹 Azelaic Acid

  • MOA: Normalises keratinisation, antibacterial, anti-inflammatory, reduces pigmentation.

  • When: Mild/moderate acne, safe in pregnancy, alternative if retinoids not tolerated.



🔹 Special Considerations

  • Pregnancy:

    • Avoid retinoids (topical or oral) and tetracyclines.

    • Azelaic acid is safe.

  • Hormonal contraception:

    • Some combined oral contraceptives (COCs) may improve acne.

    • ⚠️ The progestogen-only pill or contraceptive implant can sometimes make acne worse (NICE/NHS).

    • Always consider contraception history when evaluating acne.


🔹 Acne-like Disorders (Differentials)

  • Rosacea: No comedones; flushing, telangiectasia, papules/pustules. Triggers: alcohol, spicy food. Tx: topical metronidazole/azelaic acid, oral doxycycline.

  • Perioral dermatitis: Papules around mouth/eyes, steroid/cosmetic-induced. Tx: stop steroid, topical metronidazole or tetracycline.

  • Drug-induced eruptions: Monomorphic papules/pustules, no comedones (steroids, lithium, phenytoin).

  • Occupational acne: Chloracne, oil acne, tar acne.

  • Acne mechanica: Friction/pressure (“maskne”).

  • Acne cosmetica: Due to comedogenic products.



🔹 Key PLAB 2 Exam Takeaways

  • Comedones = hallmark of acne vulgaris.

  • Differentiate papules, pustules, nodules, cysts.

  • Oral antibiotics always with topical non-antibiotic.

  • Isotretinoin = specialist-only, strict monitoring.

  • Azelaic acid = safe in pregnancy.

  • Rosacea & drug-induced eruptions = no comedones.

  • Always assess psychosocial impact + scarring risk → early referral if severe.


In short for PLAB 2:

  • Mild → topical combos.

  • Moderate → topical + oral lymecycline/doxycycline.

  • Severe → refer for isotretinoin.

  • No comedones? Think rosacea or other mimics.

  • Check contraception history — progestogen-only methods can worsen acne.


📚References

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