Chronic recurrent follicular occlusive disease of intertriginous areas with painful nodules, abscesses, sinus tracts, and scarring.
Also known as: hidradenitis suppurativa, HS, acne inversa, Verneuil disease
Overview
A chronic, recurrent, inflammatory follicular occlusive disorder presenting with painful deep-seated nodules, abscesses, sinus tracts, and dermal scarring in intertriginous areas (axillae, inguinal, gluteal, inframammary, perianal).
Epidemiology
Prevalence ~1% (likely underestimated; often misdiagnosed for years). Female predominance 3:1. Onset typically after puberty, peak ages 20-40. Higher prevalence in African American populations and patients with obesity, smoking, and metabolic syndrome.
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Question 1DermatologyMedium
A 35-year-old male presents with a 3-year history of recurrent painful nodules in his bilateral axillae and groin that rupture and form interconnecting sinus tracts, with numerous scars from prior lesions. Examination shows tender nodules with draining sinus tracts in discrete patches separated by normal-appearing skin. Which of the following is the most likely diagnosis?
ACutaneous Crohn disease
BLymphogranuloma venereum
CEpidermoid cysts
DRecurrent furunculosis
EHidradenitis suppurativa
Reveal answer & full explanation
Correct answer: E — Hidradenitis suppurativa
ACutaneous Crohn disease
BLymphogranuloma venereum
CEpidermoid cysts
DRecurrent furunculosis
EHidradenitis suppurativa✓
Why Hidradenitis suppurativa is correct
Hidradenitis suppurativa (HS) is a chronic inflammatory skin condition of hair follicles in apocrine gland-bearing areas (axillae, groin)
Hurley staging: I = abscesses without sinus tracts or scarring; II = recurrent abscesses with sinus tracts and scarring as one or more widely separated lesions; III = diffuse or near-diffuse involvement with multiple interconnected tracts across the entire area
This patient's sinus tracts and scarring in discrete patches separated by normal-appearing skin are Hurley stage II
Why the others are wrong
Epidermoid cysts — present as discrete, mobile subcutaneous nodules with a central punctum that may rupture, but they do not form interconnecting sinus tracts or the chronic recurrent scarring pattern across apocrine-bearing regions seen here
Lymphogranuloma venereum — a sexually transmitted Chlamydia trachomatis (serovars L1–L3) infection causing a transient genital ulcer followed by tender inguinal buboes, not a years-long recurrent process of axillary/groin nodules with sinus tracts and scarring
Recurrent furunculosis — repeated Staphylococcus aureus follicular abscesses (boils) that are typically self-limited and resolve between episodes, lacking the chronic interconnecting sinus tracts, bridging scars, and bilateral apocrine distribution that define this presentation
Cutaneous Crohn disease — a reasonable thought because Crohn disease forms fistulas and sinus tracts and is associated with HS, but cutaneous Crohn disease is rare, usually accompanies known intestinal disease, and presents as perianal fistulas or granulomatous ulcers and plaques with noncaseating granulomas on biopsy, not years of recurrent nodules with tunneling tracts and bridging scars in the axillae and groin
Additional high-yield points
Hurley II–III treatment: adalimumab (Humira) was the first FDA-approved biologic for moderate-severe HS (PIONEER I/II trials); secukinumab (interleukin-17A (IL-17A) inhibitor) is also FDA-approved for HS
Surgery (wide local excision): for chronic fibrotic lesions
Question 2DermatologyMedium
A 29-year-old woman with axillary hidradenitis suppurativa has had well-controlled disease on her usual topical regimen and antiseptic washes, with only 1 to 2 flares a year. She now presents with 2 days of exquisite tenderness in the left axilla and asks for treatment that will relieve it before an event in 3 days. Examination shows a single firm, erythematous nodule about 1.5 cm across with no fluctuance, no draining tunnel, and no surrounding cellulitis or lymphangitic streaking. She is afebrile. Which of the following is the most appropriate treatment?
ASubcutaneous adalimumab
BIntralesional triamcinolone
COral doxycycline for 12 weeks
DOral cephalexin for 10 days
EOral isotretinoin 0.5 mg/kg
Reveal answer & full explanation
Correct answer: B — Intralesional triamcinolone
ASubcutaneous adalimumab
BIntralesional triamcinolone✓
COral doxycycline for 12 weeks
DOral cephalexin for 10 days
EOral isotretinoin 0.5 mg/kg
Why Intralesional triamcinolone is correct
An acute hidradenitis suppurativa (HS) nodule is mainly an inflammatory reaction to a ruptured hair follicle. Bacteria are present as secondary colonizers, but they are not the main cause of the pain and swelling.
Injecting triamcinolone acetonide 10 mg/mL into the nodule (commonly 0.2 to 1 mL, depending on size) treats that inflammation where it is. Pain and redness usually improve within 24 to 48 hours, which fits her 3-day deadline.
The North American HS Foundations guideline (Alikhan et al., JAAD 2019) and European HS guidelines both recommend intralesional corticosteroid for acute inflamed HS lesions.
Her disease is otherwise controlled, so the right move is to treat this one flare and continue her current regimen. One flare does not call for escalating her baseline therapy.
Side effects are mainly local: skin atrophy (a small depression), hypopigmentation and, less often, telangiectasia. Warn about these, especially in darker skin, where hypopigmentation shows more.
Why the others are wrong
Oral cephalexin for 10 days - This treats the nodule as a staphylococcal furuncle or abscess. An HS nodule is deep inflammation after follicular rupture, with bacteria only as secondary colonizers, so a short anti-staphylococcal course does not settle the inflammation and gives no quick relief. With no surrounding cellulitis, streaking or fever, there is no secondary soft-tissue infection for it to treat. (The trap is treating every tender red axillary nodule as a boil.)
Subcutaneous adalimumab - This is a real HS treatment, FDA-approved for moderate-to-severe disease, but it is used for frequent flares or Hurley II/III disease, usually after oral antibiotics have not been enough. Its benefit is judged over about 12 weeks, so it gives no relief before her event, and one flare in otherwise controlled disease does not justify a TNF inhibitor, with its infection risk and required tuberculosis screening. (The trap is choosing the best-known HS drug without matching it to how active the disease is.)
Oral isotretinoin 0.5 mg/kg - The comparison with acne is tempting, but HS is not acne. Isotretinoin works poorly in HS and takes months to act. It is also teratogenic, so a woman of reproductive age must enroll in iPLEDGE and use two forms of contraception. (The trap is reasoning from 'cystic lesions near hair follicles' to the drug used for nodulocystic acne.)
Oral doxycycline for 12 weeks - Doxycycline is a standard systemic HS therapy, but it is given as a weeks-long anti-inflammatory course for frequent flares or more extensive disease. It gives no quick relief of one nodule before her event, and a single flare in otherwise controlled disease does not call for escalating her baseline regimen. (The trap is matching the drug to the disease rather than to this one flare.)
Additional high-yield points
A short oral corticosteroid taper is also a guideline-accepted bridge, but it is used for a severe flare with many lesions. For a single nodule, an injection gives relief without exposing her whole body to a steroid.
Frequent flares or Hurley II/III disease call for systemic therapy: a tetracycline, clindamycin plus rifampin (a 10 to 12 week course; rifampin makes hormonal contraceptives less effective), or a biologic. The FDA has approved adalimumab, secukinumab and bimekizumab for moderate-to-severe HS.
Antibiotics do have a role in HS. They are given as longer anti-inflammatory and antimicrobial courses for recurrent or more extensive disease, or to treat true secondary cellulitis, not as a quick fix for one nodule.
Inject into the center of the nodule, not the normal skin around it, to limit atrophy. Intralesional steroid calms the flare but does not change the long-term course of the disease.
Pain control is part of HS care. NSAIDs and acetaminophen are reasonable additions while the injection takes effect.
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Recurrent painful boils in the axillae or groin = HS until proven otherwise; not 'staph infections.'
Smoking cessation is the single most impactful lifestyle intervention — strongly counsel at every visit.
Double-headed open comedones in affected areas are highly characteristic, but diagnosis rests on the three clinical criteria (typical lesions, typical sites, chronic relapsing course).
Oral antibiotics act through both anti-inflammatory and antibacterial effects — failure to respond does not mean culture-directed therapy is needed.
Long-standing perineal/buttock HS carries a real risk of cutaneous SCC — biopsy any chronic non-healing lesion.
References
USCMS 2019 — North American Clinical Management Guidelines for Hidradenitis Suppurativa (Alikhan et al., J Am Acad Dermatol 2019)
European S2k 2025 — Zouboulis CC, et al. European S2k guidelines for hidradenitis suppurativa/acne inversa part 2: Treatment. J Eur Acad Dermatol Venereol 2025;39(5):899-941
US/Canadian HS Foundations 2019 — Alikhan A, et al. North American clinical management guidelines for hidradenitis suppurativa: A publication from the United States and Canadian Hidradenitis Suppurativa Foundations. Part II: Topical, intralesional, and systemic medical management. J Am Acad Dermatol 2019;81(1):91-101
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