Chronic inflammatory disorder of the pilosebaceous unit driven by androgens, sebum, keratinization, and Cutibacterium acnes.
Also known as: acne, comedonal acne, inflammatory acne, nodulocystic acne, pimples
Overview
A chronic inflammatory disorder of the pilosebaceous unit characterized by comedones, papules, pustules, nodules, and cysts, distributed on the face, chest, and back.
Epidemiology
Affects up to 85% of adolescents; peak incidence ages 12-24. Persists into adulthood in ~25% of women and ~12% of men. More severe and scarring forms in male adolescents.
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Question 1DermatologyMedium
A 16-year-old male presents with worsening acne on the face and back despite 3 months of over-the-counter benzoyl peroxide. On examination, there are numerous open and closed comedones, inflammatory papules, pustules, and several tender deep nodules and cysts, with early pitted scarring across both cheeks and the upper back. He reports significant distress about his appearance. Which of the following is the most appropriate next step in management?
ATopical clindamycin
BOral doxycycline
COral isotretinoin
DTopical clascoterone
ETopical tretinoin
Reveal answer & full explanation
Correct answer: C — Oral isotretinoin
ATopical clindamycin
BOral doxycycline
COral isotretinoin✓
DTopical clascoterone
ETopical tretinoin
Why Oral isotretinoin is correct
This is severe nodulocystic acne with scarring — the principal indication for oral isotretinoin, a systemic retinoid (13-cis-retinoic acid)
Isotretinoin is the only acne therapy that targets all four pathogenic factors: follicular hyperkeratinization, sebum production, Cutibacterium acnes proliferation, and inflammation
Roughly 85 percent of patients achieve durable remission after a single course of 120 to 150 mg/kg cumulative dose over 15 to 20 weeks
Early scarring and failure of less aggressive therapy make prompt escalation important to prevent permanent disfigurement
Because the drug is teratogenic, enrollment in the iPLEDGE program with monthly monitoring is required, along with baseline and periodic lipid panels and liver function tests
Common adverse effects include cheilitis, dry skin, and hypertriglyceridemia
Why the others are wrong
Oral doxycycline — appropriate for moderate inflammatory acne but inadequate for nodulocystic disease that is already scarring and would not address the depth of involvement here
Topical tretinoin — a first-line agent for comedonal and mild inflammatory acne and useful adjunctively, but as a single topical agent it cannot control widespread nodular disease
Topical clindamycin — best used in combination with benzoyl peroxide for mild-to-moderate inflammatory acne; far too weak for this presentation, and clindamycin used alone also promotes bacterial resistance
Topical clascoterone — tempting because androgen-driven sebum fuels nodulocystic acne and, unlike spironolactone, which is used off-label and only in females, this topical androgen-receptor inhibitor is FDA-approved for acne in males from age 12, but as a single topical cream it cannot control widespread nodules and cysts that are already scarring the face and back
Question 2DermatologyMedium
A 25-year-old female has severe nodulocystic acne on the face, chest, and back that has failed topical benzoyl peroxide, topical retinoids, and two 3-month courses of oral antibiotics. She has no history of inflammatory bowel disease or depression. Which of the following is the most effective treatment?
AIsotretinoin
BOral prednisone
CIntralesional triamcinolone
DCombined oral contraceptive
ESpironolactone
Reveal answer & full explanation
Correct answer: A — Isotretinoin
AIsotretinoin✓
BOral prednisone
CIntralesional triamcinolone
DCombined oral contraceptive
ESpironolactone
Why Isotretinoin is correct
Isotretinoin is the most effective treatment for severe nodulocystic acne and acne unresponsive to antibiotics
Mechanism: reduces sebaceous gland size and sebum production by 70-90%, normalizes follicular keratinization, and is anti-inflammatory
Dose: 0.5-1 mg/kg/day for 16-20 weeks; cumulative dose 120-150 mg/kg for optimal outcomes
About 85% of patients achieve long-term remission after one course
Why the others are wrong
Spironolactone — is a useful adjunct for hormonal acne in females but is less effective than isotretinoin for nodulocystic disease (right-concept-wrong-drug)
Combined oral contraceptive — is an adjunct for hormonal female acne but less effective than isotretinoin for severe nodulocystic disease (undertreatment)
Intralesional triamcinolone — treats individual cystic lesions, not widespread disease across the face, chest, and back (right-tool-wrong-scope)
Oral prednisone — a systemic corticosteroid seems to solve the limited scope of intralesional injection by suppressing inflammation across the face, chest, and back; but oral corticosteroids have only adjunctive roles in acne, chiefly short courses for acne fulminans or to blunt a flare when isotretinoin is started, they do not produce lasting remission, and prolonged use can itself cause steroid acne (symptom suppression over disease control)
Additional high-yield points
iPLEDGE is mandatory; for patients who can become pregnant it requires two forms of contraception (isotretinoin is a potent teratogen) and monthly pregnancy tests
iPLEDGE does not govern LFT or lipid monitoring: check LFTs and fasting lipids at baseline and again at peak dose; routine monthly LFT and lipid checks are not needed (AAD 2024)
Common side effects: cheilitis (near universal), xerosis, epistaxis, arthralgias
Isotretinoin is contraindicated in pregnancy
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High glycemic load diet and dairy (weak association)
Pathophysiology
Four-step pathogenesis: (1) androgen-driven sebum overproduction, (2) follicular hyperkeratinization → microcomedone, (3) proliferation of Cutibacterium (Propionibacterium) acnes within the lipid-rich follicle, (4) innate immune activation via TLR-2 → perifollicular inflammation. Rupture of distended follicles spills contents into the dermis, producing inflammatory papules, pustules, nodules, and scarring.
Clinical presentation
Symptoms
Visible facial, chest, or back lesions; mild tenderness with inflammatory papules and nodules
Psychosocial distress, anxiety, depression — disproportionate to objective severity in many patients
Post-inflammatory hyperpigmentation in skin of color; erythema and scarring after resolution
Signs / physical exam
Open comedones (blackheads) — dilated follicles with oxidized keratin plug
Closed comedones (whiteheads) — small flesh-colored papules with intact follicular orifice
Inflammatory papules and pustules
Nodules and cysts (>5 mm) — risk of permanent scarring
Ice-pick, boxcar, or rolling atrophic scars; hypertrophic/keloid scars on chest, back, jaw
Classic findings
Mixed comedonal and inflammatory lesions in seborrheic distribution (forehead, nose, cheeks, chin, upper chest and back).
Differential diagnosis
Rosacea — Centrofacial erythema and telangiectasias, NO comedones, triggers include heat/alcohol/spice; onset typically age 30-50
Perioral dermatitis — Small papules/pustules around mouth sparing the vermilion border; often history of topical steroid use
Folliculitis (bacterial or Pityrosporum) — Monomorphous follicular pustules, often on trunk/shoulders; Pityrosporum responds to antifungals, not antibiotics
Acne fulminans / acne conglobata — Severe nodulocystic disease with fever, arthralgia, leukocytosis (fulminans); interconnected sinus tracts (conglobata)
Hidradenitis suppurativa — Painful nodules and sinus tracts in axillae, groin, inframammary folds; no comedones except double-headed open comedones
Drug-induced acneiform eruption — Sudden monomorphic eruption after steroids, EGFR inhibitors, lithium, isoniazid; no true comedones
Keratosis pilaris — Rough follicular papules on extensor arms, thighs, cheeks; no inflammation or pustules
Diagnostic workup
Diagnostic criteria
Clinical diagnosis based on lesion morphology and distribution. Severity graded as mild (comedonal ± few inflammatory papules), moderate (numerous papules/pustules ± few nodules), or severe (widespread nodulocystic disease, scarring, or failure of prior therapy).
Labs
Generally clinical diagnosis — no routine labs
If suspect hyperandrogenism (sudden severe acne, hirsutism, menstrual irregularity, alopecia): total/free testosterone, DHEAS, 17-OH progesterone, LH/FSH ratio, prolactin
Baseline LFTs and lipid panel before starting isotretinoin; pregnancy testing per iPLEDGE program
Imaging
Not indicated for routine acne
Pelvic ultrasound if PCOS suspected
Diagnostic algorithm
Severity
Lesion Profile
Stepwise Therapy
Mild comedonal
Open/closed comedones, few papules
Topical retinoid ± BPO
Mild-moderate inflammatory
Numerous papules/pustules
Topical retinoid + BPO + topical antibiotic
Moderate
Papules, pustules, few nodules, truncal involvement
Oral isotretinoin (iPLEDGE) ± short steroid course
Severity-based stepwise therapy for acne vulgaris (AAD 2024).
Treatment
First-line
Mild comedonal: topical retinoid — tretinoin 0.025-0.1%, adapalene 0.1-0.3%, tazarotene 0.05-0.1% (apply at night; avoid all topical retinoids in pregnancy — tazarotene is contraindicated; start every other night to limit irritation)
Moderate: add oral antibiotic for 3-4 months — doxycycline 50-100 mg BID or minocycline 50-100 mg BID (sarecycline as alternative); avoid in children <8 yrs and pregnancy
Hormonal therapy in women: combined oral contraceptive (norgestimate/ethinyl estradiol, drospirenone/EE) or spironolactone 50-200 mg/day (routine K+ monitoring unnecessary in healthy young women; avoid in pregnancy — antiandrogen that can feminize a male fetus)
Severe nodulocystic / scarring / treatment-refractory
iPLEDGE enrollment required — monthly pregnancy tests and 2 forms of contraception in females of reproductive potential
Check LFTs and fasting lipids at baseline and at peak dose (routine CBC and monthly labs not needed); counsel on dryness, photosensitivity, depression/mood changes, IBD signal (debated)
Mechanism: oral retinoid that shrinks sebaceous glands and cuts sebum output about 70-90%, normalizes follicular keratinization, and indirectly reduces C. acnes and inflammation; the only agent acting on all four pathogenic factors
Acne fulminans
Systemic corticosteroids (prednisone 0.5-1 mg/kg/day) for 4-6 weeks, then overlap with low-dose isotretinoin starting at 0.1 mg/kg/day and titrate
Pregnancy
Azelaic acid 20% and/or benzoyl peroxide; topical clindamycin or erythromycin only in combination with BPO
Avoid all retinoids (topical and oral), tetracyclines, and spironolactone; if a systemic antibiotic is truly needed, use cephalexin or a macrolide (erythromycin, azithromycin)
Second-line / adjunct
Topical clascoterone 1% cream BID — first topical androgen receptor inhibitor approved for acne
Topical dapsone 5-7.5% — useful in adult female acne
Azelaic acid 15-20% — antimicrobial, anti-inflammatory, brightening (helpful for PIH)
Intralesional triamcinolone 2.5-5 mg/mL for individual nodules/cysts
Procedural: chemical peels, light/laser therapy, comedone extraction; scar revision with subcision, microneedling, fractional laser, dermabrasion, fillers
Comedones are the pathognomonic primary lesion of acne — their absence should prompt reconsideration of the diagnosis (especially rosacea or folliculitis).
Never combine isotretinoin with tetracyclines — risk of pseudotumor cerebri.
Spironolactone is the most underused effective therapy for adult female acne; do not require routine K+ monitoring in healthy young women on stable doses (AAD 2024 update).
Topical retinoids are foundational at every severity tier and during maintenance — do not stop them when adding other therapies.
Sudden-onset severe acne with hirsutism or virilization in an adult woman warrants endocrine workup for ovarian or adrenal tumor.
References
AAD 2024 — Guidelines of Care for the Management of Acne Vulgaris (Reynolds et al., J Am Acad Dermatol 2024)
Global Alliance 2018 — Practical Management of Acne for Clinicians: An International Consensus from the Global Alliance to Improve Outcomes in Acne (Thiboutot et al., J Am Acad Dermatol 2018)
iPLEDGE — iPLEDGE Risk Evaluation and Mitigation Strategy (REMS) Program — US FDA
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