What is the most likely diagnosis for a Black male presenting with painful pustular lesions on the legs, abdomen, and buttocks?

Diagnosis: Folliculitis or Furuncles (Most Likely Staphylococcus aureus)

The most likely diagnosis for a Black male presenting with painful pustular lesions on the legs, abdomen, and buttocks is bacterial folliculitis or furuncles caused by Staphylococcus aureus. 1

Clinical Reasoning

Primary Diagnostic Considerations

The distribution pattern (legs, abdomen, buttocks) combined with painful pustules strongly suggests a staphylococcal follicular infection rather than other differential diagnoses:

• Furuncles (boils) are infections of hair follicles caused by S. aureus, where suppuration extends through the dermis into subcutaneous tissue, forming small abscesses. 1 These present as inflammatory nodules with overlying pustules and are characteristically painful. 1

• The anatomic distribution involving legs and buttocks is classic for chronic folliculitis patterns, particularly dermatitis cruris pustulosa et atrophicans (DCPA), which predominantly affects the lower limbs and can extend to trunk areas. 2 This condition shows symmetric leg involvement in 81.1% of cases and can involve abdomen in 29.73% of patients. 2

• S. aureus is isolated from pustular follicular lesions in 86.49% of cases in similar presentations, with 56.75% of patients being carriers at multiple body sites (nares, axillae, gluteal fold). 2

Key Distinguishing Features

• Furuncles differ from simple folliculitis by deeper extension beyond the hair follicle, creating painful, tender nodules rather than superficial pustules. 1 The pain component in your patient strongly suggests furuncles rather than superficial folliculitis. 1

• Multiple lesions involving legs, abdomen, and buttocks indicate either multiple furuncles or a carbuncle (interconnected furuncles draining through multiple skin openings). 1, 3

• Pustules with surrounding erythema and pain, particularly on the trunk and extremities, point to staphylococcal rather than streptococcal etiology. 4 Staphylococcal infections characteristically produce pustules with narrow erythema rims, while streptococcal infections cause spreading erythema with little purulence. 4

Important Differential Diagnoses to Exclude

Pyoderma Gangrenosum (Less Likely but Critical to Rule Out)

• Pyoderma gangrenosum presents with rapidly developing, painful skin ulcers (not pustules initially) and affects lower extremities in 70-79% of cases. 5, 6 However, it begins as erythematous papules or pustules before progressing to deep excavating ulcerations. 6

• This diagnosis is less likely given the absence of mentioned ulceration, but must be considered if lesions progress or fail to respond to antibiotics. 5, 6 Pyoderma gangrenosum is associated with inflammatory bowel disease in 50-70% of cases. 5, 7

• Key distinguishing feature: Pyoderma gangrenosum lesions contain purulent material that is STERILE on culture unless secondarily infected, whereas bacterial folliculitis/furuncles will culture S. aureus. 6

Impetigo (Less Likely Given Distribution)

• Impetigo typically affects exposed areas (face and extremities) rather than covered areas like abdomen and buttocks. 1 The painful pustular nature also argues against impetigo, which is usually not described as particularly painful. 1

Diagnostic Approach

Immediate Clinical Assessment

• Examine for fluctuance, which indicates abscess formation requiring incision and drainage. 1 Furuncles and carbuncles are fluctuant red nodules surrounded by erythematous swelling. 1

• Assess for "wooden-hard" subcutaneous tissues, which would indicate necrotizing fasciitis—a surgical emergency. 1 In simple cellulitis or folliculitis, subcutaneous tissues remain yielding on palpation. 1

• Check for systemic symptoms (fever, hypotension, altered mental status) that would necessitate hospitalization and broad-spectrum IV antibiotics. 1

Microbiological Workup

• Culture pus from pustules to identify the pathogen and determine antibiotic susceptibilities, particularly for methicillin-resistant S. aureus (MRSA). 1, 8 This is especially important in recurrent or treatment-resistant cases. 8

• Consider screening carrier sites (anterior nares, axillae, gluteal fold) if recurrent infections occur, as 56.75% of patients with chronic folliculitis are S. aureus carriers. 2

When to Biopsy

• Biopsy is NOT routinely needed for typical bacterial folliculitis/furuncles. 1

• However, biopsy from the periphery of lesions is indicated if: 1, 6

  • Lesions fail to respond to adequate antibiotic therapy
  • Rapid progression to ulceration occurs (suggesting pyoderma gangrenosum)
  • There is suspicion of underlying systemic disease

Treatment Algorithm

For Localized Furuncles/Folliculitis

• Incision and drainage is the primary treatment for fluctuant abscesses and furuncles. 1 Simply covering with dry dressing is usually most effective, though some clinicians pack with gauze. 1

• Systemic antibiotics are NOT routinely necessary after incision and drainage unless: 1, 8

  • Multiple lesions are present
  • Extensive surrounding cellulitis exists
  • Severe systemic manifestations (high fever) occur
  • Patient has severely impaired host defenses

Antibiotic Selection When Indicated

• For simple folliculitis without abscess formation, topical benzoyl peroxide is first-line nonantibiotic treatment. 8 Topical mupirocin or clindamycin are antibiotic alternatives. 8

• For treatment-resistant folliculitis or multiple furuncles requiring systemic therapy, oral cephalexin or dicloxacillin is appropriate for methicillin-susceptible S. aureus. 8

• MRSA coverage should be considered if infections have not improved with initial treatment. 8 Options include trimethoprim-sulfamethoxazole, doxycycline, or clindamycin based on local resistance patterns.

For Recurrent Disease

• Address predisposing factors including use of occlusive synthetic clothing (particularly full-length trousers), occupational irritant exposure, and seasonal aggravation. 2 These factors were present in the majority of chronic folliculitis cases. 2

• Consider decolonization protocols if S. aureus carrier status is confirmed, though evidence for this approach is limited. 2

Critical Pitfalls to Avoid

• Do NOT prescribe antibiotics alone for fluctuant abscesses—incision and drainage is essential. 1 Antibiotics without drainage will fail.

• Do NOT assume all pustular lesions are infectious. 5, 6 If lesions rapidly progress to ulceration despite antibiotics, or if cultures are sterile, strongly consider pyoderma gangrenosum and screen for inflammatory bowel disease. 5, 6, 7

• Do NOT miss necrotizing fasciitis. 1 The presence of wooden-hard subcutaneous tissues, rapid progression, systemic toxicity, or skin anesthesia requires immediate surgical consultation. 1

• Do NOT overlook associated systemic disease. 5, 7 If pyoderma gangrenosum is confirmed, 50-70% of patients have underlying conditions (inflammatory bowel disease, hematologic malignancies, rheumatologic disorders). 5