What is the difference between dissecting cellulitis of the scalp and bacterial cellulitis of the scalp regarding diagnosis and management?

Dissecting Cellulitis vs. Bacterial Cellulitis of the Scalp: Diagnosis and Management

Dissecting cellulitis of the scalp and bacterial cellulitis of the scalp are fundamentally different diseases requiring completely different management approaches—dissecting cellulitis is a chronic inflammatory follicular occlusion disorder treated with immunosuppression and surgery, while bacterial cellulitis is an acute infectious process requiring antibiotics.

Key Diagnostic Differences

Clinical Presentation

Dissecting Cellulitis of the Scalp:

• Chronic, recurrent painful nodules and abscesses that interconnect via sinus tracts, leading to scarring alopecia 1, 2
• Suppurative lesions with follicular and perifollicular inflammation that undermine the scalp 1
• Progressive course over months to years with disfiguring, purulent lesions 3
• Often associated with hidradenitis suppurativa and conglobate acne (follicular occlusion triad) 4
• Represents a neutrophilic inflammatory disorder, not a primary infection 2

Bacterial Cellulitis of the Scalp:

• Acute onset of erythema, warmth, swelling, and tenderness spreading diffusely across the scalp 5
• Typically unilateral with well-demarcated borders of erythema 5
• Systemic signs may include fever, tachycardia, and leukocytosis 6
• Caused by streptococci (primarily Group A) or methicillin-sensitive S. aureus in >80% of cases 6
• Pathogen isolation rate <20% in nonpurulent cellulitis 6

Diagnostic Workup

Dissecting Cellulitis:

• Clinical diagnosis based on characteristic chronic nodules, sinus tracts, and scarring alopecia 1, 2
• Skin biopsy shows neutrophilic inflammation with follicular rupture and abscess formation despite absence of bacterial infection 2
• Cultures typically negative or show colonizing organisms, not causative pathogens 2

Bacterial Cellulitis:

• Clinical diagnosis in most cases without need for cultures 6
• Blood cultures indicated only if systemic toxicity, immunocompromise, or malignancy present (positive in only 5% of cases) 5
• Tissue aspiration or biopsy reserved for high-risk populations or treatment failure 7

Management Differences

Bacterial Cellulitis Treatment Algorithm

First-Line Therapy:

• Cephalexin 500 mg every 6 hours orally for 5 days if clinical improvement occurs 5, 7
• Alternative: Dicloxacin or amoxicillin-clavulanate for similar duration 5, 7
• Extend beyond 5 days ONLY if infection has not improved 5, 7

MRSA Coverage (Add ONLY if specific risk factors present):

• Penetrating trauma, purulent drainage, injection drug use, known MRSA colonization, or systemic inflammatory response syndrome 5, 7
• Options: Clindamycin alone OR trimethoprim-sulfamethoxazole plus a beta-lactam 5, 7

Hospitalization Criteria:

• Systemic toxicity (fever, hypotension, altered mental status) 5, 7
• Concern for necrotizing infection or deeper involvement 7
• Failure of outpatient therapy after 24-48 hours 7

Adjunctive Measures:

• Elevate affected area to promote drainage 5, 7
• Treat predisposing conditions (tinea, trauma, venous insufficiency) 6, 5

Dissecting Cellulitis Treatment Algorithm

Initial Management (Mild-Moderate Disease):

• Oral isotretinoin combined with rifampicin represents a first-line approach for active disease 1
• Intralesional or topical corticosteroids for localized lesions 3
• Oral antibiotics (tetracyclines, clindamycin) provide limited benefit but may reduce secondary bacterial colonization 3

Refractory Disease (Failed Standard Therapy):

• TNF-α inhibitors (adalimumab) demonstrate superior efficacy for controlling inflammation and preventing progression 8, 2, 3
• Adalimumab controls inflammation rapidly but relapse occurs on discontinuation if structural disease persists 2
• IL-17 inhibitors (secukinumab) show promise for severe cases, especially when associated with hidradenitis suppurativa 4

Definitive Treatment Options:

• Laser therapy (CO2 or Nd:YAG) shows better remission rates than medical therapy alone 3
• Surgical excision of involved areas provides highest remission rates but carries significant morbidity 3
• X-ray epilation demonstrates excellent remission but has serious long-term complications 3

Proposed Treatment Algorithm for Refractory Cases:

1. Trial of isotretinoin plus rifampicin for 3-6 months 1, 3
2. If inadequate response, initiate TNF-α inhibitor (adalimumab) 8, 2, 3
3. Consider laser therapy or surgical excision for localized persistent disease 3
4. Continuous biologic therapy may be necessary to prevent relapse 2

Critical Pitfalls to Avoid

For Bacterial Cellulitis:

• Do NOT routinely add MRSA coverage without specific risk factors—MRSA is uncommon in typical cellulitis even in high-prevalence settings 5, 7
• Do NOT extend treatment beyond 5 days automatically; extend only if no clinical improvement 5, 7
• Do NOT delay surgical consultation if necrotizing infection suspected (severe pain, rapid progression, systemic toxicity) 7

For Dissecting Cellulitis:

• Do NOT treat with antibiotics alone as primary therapy—this is an inflammatory disorder, not a bacterial infection 2, 3
• Do NOT expect permanent resolution with isotretinoin monotherapy—response is limited and relapse common 3
• Do NOT discontinue biologic therapy prematurely—relapse is expected if structural disease persists 2
• Do NOT delay consideration of surgical excision in localized refractory disease—medical therapy alone rarely achieves permanent remission 3

Key Distinguishing Features Summary

Feature	Dissecting Cellulitis	Bacterial Cellulitis
Onset	Chronic, progressive [1,2]	Acute, rapid [5]
Pathophysiology	Follicular occlusion with sterile inflammation [2]	Bacterial infection (streptococci/staph) [6,5]
Primary Treatment	Immunosuppression (biologics, isotretinoin) [8,2,3]	Antibiotics (beta-lactams) [5,7]
Duration	Months to years, often lifelong [2,3]	5-7 days if responsive [5,7]
Scarring	Permanent scarring alopecia [1,2]	Typically resolves without scarring [5]
Recurrence	Expected without continuous therapy [2]	Uncommon unless predisposing factors persist [6]