What is the most appropriate final diagnosis for a diabetic adult with a long‑standing epidermal inclusion cyst on the right posterior shoulder that has now become a deep abscess with radiating pain and systemic malaise, suggesting possible necrotizing fasciitis?

Necrotizing Fasciitis with Secondary Infection of Epidermal Inclusion Cyst

The most appropriate final diagnosis for this case is necrotizing fasciitis (NF) secondary to an infected epidermal inclusion cyst in a diabetic patient. This diagnosis is supported by the clinical triad of deep abscess formation, radiating pain, and systemic malaise in a high-risk diabetic host with a known skin lesion that has transformed from a chronic, stable condition into an acute, life-threatening infection. 1

Diagnostic Rationale

Key Clinical Features Supporting Necrotizing Fasciitis

The presentation meets multiple cardinal diagnostic criteria for NF:

• Radiating pain suggests extension beyond superficial tissues and likely represents the hallmark "pain disproportionate to physical findings" that distinguishes NF from simple cellulitis or abscess 1, 2, 3
• Deep abscess formation from a previously stable epidermal inclusion cyst indicates progression to deeper tissue planes involving fascia 1
• Systemic malaise reflects the systemic toxicity characteristic of NF, which can progress to altered mental status, fever, and hypotension 1, 3
• Diabetes mellitus is the single most important risk factor for developing NF and is associated with atypical presentations that lead to delayed diagnosis 4, 5, 6

Classification and Microbiology

This case most likely represents Type 1 (polymicrobial) necrotizing fasciitis, which accounts for the majority of cases arising from skin lesions in diabetic patients. 1, 4 Type 1 NF typically involves:

• Mixed aerobic and anaerobic organisms (average of 5 pathogens per wound) 1
• Organisms originating from skin flora that gain entry through the compromised epidermal inclusion cyst 1
• Common pathogens include coliforms, anaerobic bacteria, and anaerobic Streptococcus species 1

Critical Distinguishing Features from Alternative Diagnoses

Why this is NOT simply a complicated abscess:

• True abscesses have localized fluctuance and discrete pus collections that respond to incision and drainage alone 7
• NF characteristically shows "no true pus even during deep dissection," only a thin, brownish exudate 1, 7
• The radiating pain pattern suggests fascial plane involvement extending beyond a localized collection 1, 3

Why this is NOT simple cellulitis:

• Cellulitis typically responds to initial antibiotic therapy within 24-48 hours 3, 7
• The hard, "wooden feel" of subcutaneous tissue extending beyond visible skin involvement is pathognomonic for NF 1, 3
• Cellulitis lacks the deep tissue involvement and systemic toxicity seen here 1, 7

Diagnostic Approach in Philippine Hospital Setting

Immediate Clinical Assessment (Do Not Delay for Imaging)

Clinical judgment is the most important diagnostic element and imaging should never delay surgical consultation when NF is suspected. 1, 3 Assess for:

1. Pain characteristics: Severity disproportionate to examination findings 2, 3, 6
2. Tissue consistency: Hard, wooden feel extending beyond apparent involvement 1, 3
3. Extent of involvement: Edema or tenderness beyond visible erythema (present in 80% of NF cases) 7
4. Skin changes: Look for bullous lesions, skin necrosis, or ecchymoses (though these are late findings present in only 0-5% initially) 3, 7
5. Crepitus: Highly specific but present in minority of early cases 3, 7
6. Systemic signs: Fever, tachycardia, hypotension, altered mental status 1, 3

Laboratory Risk Stratification (Adjunctive Only)

The LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score can help stratify risk but has poor sensitivity (68.2% for ≥6,40.8% for ≥8) and should never be used to rule out NF. 2, 3, 7 A score ≥6 suggests NF; ≥8 indicates 75% risk. 2

Critical pitfall: Normal laboratory values do not exclude NF, and waiting for results delays life-saving intervention. 3, 7

Imaging (Only if Patient is Stable and Diagnosis Uncertain)

• CT scan with IV contrast: 100% sensitivity, 81% specificity for NF 3, 7
  • Look for: fat stranding, fluid/gas along fascial planes, fascial thickening, non-enhancing fascia 3
• Bedside ultrasound: 88.2% sensitivity, 93.3% specificity 3
  • Look for: diffuse subcutaneous thickening with fluid >4mm along deep fascia 3

However, requesting imaging may delay definitive diagnosis and treatment when clinical suspicion is high. 1, 3

Definitive Diagnosis: Surgical Exploration

Immediate surgical consultation is mandatory as delays directly correlate with mortality. 2, 3 Each hour of delay increases mortality risk. 7

Intraoperative findings confirming NF: 1, 3

• Fascia appears swollen and dull gray with stringy areas of necrosis
• Thin, brownish "dishwater" exudate (not true pus)
• Extensive undermining of surrounding tissues
• Tissue planes dissect easily with gloved finger or blunt instrument
• Minimal bleeding and resistance to finger dissection

The "Finger Test": If diagnosis is uncertain, perform a 2-cm exploratory incision down to deep fascia under local anesthesia. 3, 7 Positive findings include minimal resistance to dissection, lack of bleeding, necrotic tissue, and murky gray fluid. 7

Management Implications for Mortality and Morbidity

Surgical Source Control (Priority #1)

Aggressive surgical debridement is the major therapeutic modality and must be achieved within the first 12 hours of admission. 1, 7 The decision to operate should be based on: 1

1. No response to antibiotics after reasonable trial
2. Profound toxicity, fever, hypotension, or advancement during antibiotic therapy
3. Any skin necrosis with easy fascial dissection
4. Gas in affected tissues

Serial debridements every 24-36 hours are necessary until no further necrotic tissue remains. 1, 2 Most patients should return to the operating room daily until the surgical team finds no further need for debridement. 1

Antibiotic Therapy

Broad-spectrum coverage for polymicrobial Type 1 NF (appropriate for this diabetic patient with skin-source infection): 2

• Vancomycin, linezolid, or daptomycin (for Gram-positive coverage including MRSA)
• PLUS piperacillin-tazobactam, a carbapenem, OR ceftriaxone plus metronidazole (for Gram-negative and anaerobic coverage)

Obtain Gram stain of deep tissue exudate immediately during exploration and culture specimens from deep tissues (not superficial wound). 3 Blood cultures should be obtained. 3

Supportive Care

• Aggressive fluid resuscitation due to copious tissue fluid losses 2
• Intensive monitoring for sepsis 7
• Glycemic control (critical in diabetic patients) 4
• Nutritional support 4
• Hemodynamic stabilization 4

Prognosis and Risk Factors

Mortality in diabetic patients with NF is significantly elevated, approaching 50-70% when hypotension and organ failure develop. 1, 7 The mortality rate is directly proportional to time to intervention. 8

Diabetes-specific considerations: 4, 5

• Immunocompromised and neuropathic diabetic patients present with atypical symptomatology
• High percentage of misdiagnosed cases in emergency departments
• Worse outcomes compared to non-diabetic patients
• Increased risk of limb loss

Common Diagnostic Pitfalls to Avoid

1. Relying on absence of crepitus or skin necrosis to exclude NF—these are late signs 3
2. Waiting for imaging results before surgical consultation when clinical suspicion is high 1, 3
3. Using LRINEC score alone to rule out NF due to inadequate sensitivity 3, 7
4. Treating as simple cellulitis or abscess and waiting 24-48 hours to reassess—this delay is fatal in NF 3, 7
5. Assuming superficial wound cultures reflect deep tissue infection—they do not 1

Final Diagnosis Statement for Philippine Hospital Documentation

Primary Diagnosis: Necrotizing Fasciitis, Type 1 (Polymicrobial), Right Posterior Shoulder

Secondary Diagnoses:

• Infected Epidermal Inclusion Cyst (source of infection)
• Type 2 Diabetes Mellitus (predisposing factor)

Classification: Eron Class 4 (sepsis syndrome and life-threatening infection) 1 or WSES Classification: Necrotizing SSTI 1

This diagnosis appropriately captures the severity, guides aggressive surgical and medical management, and communicates the life-threatening nature of the condition to all members of the healthcare team, which is essential for reducing morbidity and mortality in this high-risk diabetic patient.