What is the most likely cause of recurrent painful subcutaneous nodules in the right axilla of a 45‑year‑old male smoker who works as a roofer?

Hidradenitis Suppurativa: Obstruction of Folliculopilosebaceous Units

The most likely cause of this patient's recurrent painful subcutaneous nodules in the axilla is obstruction of folliculopilosebaceous units (Answer D), consistent with hidradenitis suppurativa (HS). 1, 2

Pathophysiology

The central pathogenic event in HS is occlusion of the upper part of the folliculopilosebaceous unit, leading to rupture of the sebofollicular canal with consequent perifollicular lymphohistiocytic inflammation. 1, 2 This is fundamentally a disease of the follicular epithelium rather than the apocrine or eccrine sweat glands, making options A and B incorrect. 3

• Follicular occlusion is the primary event: Constant mechanical forces (pressure and friction) lead to follicular enlargement, dilatation, microtears, and ruptures with ensuing abscesses. 3
• The disease progresses from follicular inflammation to the characteristic painful nodules, abscesses, sinus tracts, and scarring seen in established HS. 1

Clinical Presentation Matching This Case

This patient's presentation is classic for HS:

• Location: Axillary region is one of the most common sites, along with inguinal and anogenital areas (apocrine gland-bearing intertriginous regions). 4, 1
• Lesion characteristics: Recurrent, painful, tender subcutaneous nodules are the hallmark early manifestations. 5, 4
• Demographics: 45-year-old male with postpubertal onset fits the typical age range. 4
• Smoking history: The pack-per-day smoking habit is highly significant—there is a highly significant association between HS prevalence and current smoking (Odds ratio 12.55). 2
• Occupational factors: Working as a roofer involves significant mechanical stress, friction, and pressure in axillary areas from repetitive arm movements and equipment, which can contribute to follicular occlusion. 3

Why Other Options Are Incorrect

Option A (Bacterial proliferation in eccrine sweat glands) is incorrect because HS does not primarily involve eccrine glands, and bacterial proliferation is a secondary phenomenon, not the primary cause. 1

Option B (Immune response to Cutibacterium acnes) describes the pathophysiology of acne vulgaris, not HS. While HS involves immune dysregulation and secondary bacterial colonization, the primary event is follicular occlusion, not an immune response to C. acnes. 4, 1

Option C (Malignant transformation of epithelial cells) would present differently with progressive, non-recurrent masses, systemic symptoms, and different imaging characteristics—not the recurrent inflammatory nodules seen here. 6

Critical Diagnostic Considerations

• HS is often misdiagnosed or delayed in diagnosis due to disease unawareness among physicians, leading to years of unnecessary suffering. 4
• The 6-month duration of recurrent lesions in the same location (right axilla) is typical for HS rather than simple folliculitis or furunculosis. 5
• Cultures typically show commensal skin flora and mixed anaerobic bacteria, which are secondary colonizers, not primary pathogens. 3

Clinical Pitfall to Avoid

Do not mistake HS for simple recurrent bacterial abscesses or furunculosis. The recurrent nature in characteristic locations (axillae, groin), association with smoking, and chronic inflammatory course distinguish HS from primary bacterial infections. 4, 2 The absence of systemic signs and the localized, recurrent pattern also argue against disseminated infections like atypical mycobacteria, which would present with multiple subcutaneous nodules in immunocompromised patients. 6