INFLAMMATORY AND IMMUNE-MEDIATED SKIN DISORDERS

Acne Vulgaris

Etiology and risk factors

• Androgen-sensitive sebum production, follicular occlusion, Cutibacterium acnes, and inflammation interact. Genetic susceptibility is common (Gohara et al., 2012; Pincus & McCalmont, 2019).
• Adolescence is typical, but neonatal and adult disease occur. Occlusive products or equipment, friction, hormonal disorders, and medications such as systemic corticosteroids, lithium, and selected anticonvulsants may worsen acne or cause acneiform eruptions (Gohara et al., 2012; Pincus & McCalmont, 2019).

Pathophysiology

• Abnormal keratinization plugs the follicular infundibulum, producing a microcomedone. Sebum accumulates and C. acnes proliferates in the anaerobic follicle (Norris, 2020; Pincus & McCalmont, 2019).
• Innate immune signaling and follicular-wall rupture produce papules, pustules, nodules, cyst-like lesions, postinflammatory pigment change, and scar (Norris, 2020; Pincus & McCalmont, 2019).

Clinical manifestations

• Open and closed comedones on face, chest, shoulders, and back; inflammatory papules/pustules; deeper nodules; tenderness; postinflammatory hyperpigmentation; atrophic or hypertrophic scars (Gohara et al., 2012; Pincus & McCalmont, 2019).
• Adult women may have jawline/lower-face disease. Abrupt severe acne with fever or arthralgia suggests acne fulminans (Gohara et al., 2012; Pincus & McCalmont, 2019).

Findings that argue against or redirect

• Absence of comedones redirects toward rosacea, perioral dermatitis, or folliculitis (Gohara et al., 2012; Pincus & McCalmont, 2019).
• Monomorphic lesions after a medication or occlusive exposure suggest acneiform eruption. Marked hirsutism, irregular menses, virilization, or rapid onset suggests hyperandrogenism (Gohara et al., 2012; Pincus & McCalmont, 2019).
• Culture is not routinely needed; use it when gram-negative folliculitis or unusual infection is suspected (Gohara et al., 2012; Pincus & McCalmont, 2019).

Diagnostic evaluation

• Diagnosis and severity grading are clinical. Document lesion types, distribution, scarring, pigment change, psychosocial impact, current skin products, medication exposures, and pregnancy potential (Gohara et al., 2012; Pincus & McCalmont, 2019).
• Order endocrine testing only when clinical findings suggest hyperandrogenism. Confirm pregnancy status and follow the safeguards required for teratogenic therapy (Gohara et al., 2012; Pincus & McCalmont, 2019).

Expected diagnostic and laboratory findings

• No routine laboratory finding confirms acne. Comedones plus the typical distribution are the major diagnostic features (Gohara et al., 2012; Pincus & McCalmont, 2019).
• Histology, rarely needed, shows follicular hyperkeratinization, inflammation, and rupture. A bacterial culture may identify gram-negative folliculitis when treatment response is atypical (Gohara et al., 2012; Pincus & McCalmont, 2019).

Differential diagnosis

• Rosacea: central facial erythema/flushing/telangiectasia and papules/pustules without comedones (Gohara et al., 2012; Pincus & McCalmont, 2019).
• Folliculitis: monomorphic follicular pustules, often itchy, with organism or exposure clues (Gohara et al., 2012; Pincus & McCalmont, 2019).
• Perioral dermatitis: periorificial papules with vermilion sparing and no comedones (Gohara et al., 2012; Pincus & McCalmont, 2019).
• Medication-induced acneiform eruption: sudden monomorphic papules/pustules temporally related to systemic therapy (Gohara et al., 2012; Pincus & McCalmont, 2019).

Treatment and management

• Use multimodal topical therapy that combines complementary mechanisms. Benzoyl peroxide, topical retinoids, and topical antibiotics are strongly recommended options; azelaic acid, salicylic acid, and clascoterone are conditional options for selected patients (Pincus & McCalmont, 2019; Reynolds et al., 2024).
• For moderate to severe inflammatory acne, doxycycline is a strongly recommended systemic option. Limit systemic antibiotic duration and combine the antibiotic with benzoyl peroxide and other topical therapy to reduce resistance and maintain response (Pincus & McCalmont, 2019; Reynolds et al., 2024).
• Combined oral contraceptives or spironolactone may benefit selected patients. Isotretinoin is strongly recommended for severe acne, acne causing scarring or major psychosocial burden, or acne that has failed standard oral or topical therapy. Follow all pregnancy-prevention and monitoring requirements (Pincus & McCalmont, 2019; Reynolds et al., 2024).
• Use gentle noncomedogenic skin care and address dyspigmentation, scarring, and psychosocial effects early (Pincus & McCalmont, 2019; Reynolds et al., 2024).

Additional complications and red flags

• Pregnancy status materially changes treatment selection because retinoids can cause fetal harm (Gohara et al., 2012; Pincus & McCalmont, 2019).

---

---

References

Gohara, M. A., Schaffer, J. V., Abbasi, N. R., Kingsley, M. M., Sheehan, J. M., & Arndt, K. A. (2012). Inflammatory dermatoses (rashes). In M. C. Henderson, L. M. Tierney, Jr., & G. W. Smetana (Eds.), The patient history: An evidence-based approach to differential diagnosis (2nd ed.). McGraw-Hill.

Norris, T. L. (2020). Porth’s essentials of pathophysiology (5th ed.). Wolters Kluwer.

Pincus, L. B., & McCalmont, T. H. (2019). Diseases of the skin. In G. D. Hammer & S. J. McPhee (Eds.), Pathophysiology of disease: An introduction to clinical medicine (8th ed.). McGraw-Hill Education.

Reynolds, R. V., Yeung, H., Cheng, C. E., Cook-Bolden, F., Desai, S. R., Druby, K. M., Freeman, E. E., Keri, J. E., Stein Gold, L. F., Tan, J. K. L., Tollefson, M. M., Weiss, J. S., Wu, P. A., Zaenglein, A. L., Han, J. M., & Barbieri, J. S. (2024). Guidelines of care for the management of acne vulgaris. Journal of the American Academy of Dermatology, 90(5), 1006.e1–1006.e30. https://doi.org/10.1016/j.jaad.2023.12.017