Cultures remained negative, and broad-spectrum antibiotics were administered. A ct scan ruled out nf, showing infection confined to subcutaneous tissue without fascial involvement, specifically absence of deep plane infiltration, emphysema or organized collections (figure 2).


Figure 2: ct scan of right leg Signs of subcutaneous tissue densification without collections or deep-tissue gas formation

Multidisciplinary discussions among pediatrics, infectious diseases, dermatology and plastic surgery teams deferred surgical debridement. A skin biopsy was performed to investigate nds and corticosteroids (prednisolone 30 mg iv every 12 hours) were initiated. Wound care included flaminal^®, allevyn^® and mepilex^® dressings (figure 3).


Figure 3: wound care Progressive resolution of skin lesions with frequent dressings

Over two weeks, the patient’s condition improved. Biopsy results confirmed nnd, showing neutrophilic infiltrate, vasculitis and necrosis. After 45 days of hospitalization, the patient was discharged on prednisolone and cyclosporine, with follow-up care. Scarring was evident but improved progressively (figure 4).


Figure 4: 8 months after hospital discharge
Secondary healing with scarring of previous wounds

Discussion
Diagnosing nds is challenging due to their rarity and clinical overlap with nf^1,7. Both conditions present with progressive skin lesions, fever, leukocytosis, and systemic inflammatory markers involving necrosis of tissues^8,9. Distinguishing between these entities is crucial for appropriate treatment, as one is primarily infectious and the other is inflammatory. Nf, however, often involves deep tissue destruction and requires emergent surgical debridement^10,11. In contrast, nds are treated with systemic corticosteroids and conservative wound care^10,12. Pathergy is a key differentiator, as trauma-induced lesions in nds may worsen with surgical interventions⁸.

Nf is infectious in origin, often followed by trauma and caused by bacteria as streptococcus pyogenes, staphylococcus aureus (including mrsa), clostridium species, or polymicrobial infections^11,13. Clinical presentation is a rapidly progressing infection of the fascia and subcutaneous tissue with systemic toxicity, severe pain out of proportion, skin changes with eventual necrosis, fever, tachycardia, hypotension and multi-organ dysfunction in advanced cases^11,13. Bacterial toxins and enzymes cause tissue destruction, vascular occlusion and necrosis and systemic inflammatory response can lead to septic shock¹³.

Histopathology shows necrosis with neutrophilic infiltration and presence of bacteria in tissue samples. Surgical exploration for confirmation and positive cultures is the current diagnostic criteria¹³. Treatment needs emergent surgical debridement, broad-spectrum antibiotics and supportive care^7,11,13.

Nnd is an inflammatory condition, non-infectious in nature associated with immune dysregulation or underlying systemic or inflammatory disorders⁹. Clinical presentation is a progressive painful skin necrotic plaques, nodules or ulcers, resembling nf but without signs of systemic infection^6,10. Immunemediated neutrophilic infiltration cause tissue necrosis without pathogen involvement and histopathology shows neutrophilic infiltrate with tissue necrosis without organisms^5,9. Diagnosis is based on clinical suspicion with exclusion of infectious causes such as nf and biopsy with absence of infection and no microbial growth^2,6,12. Treatment involves high-dose systemic corticosteroids, immunosuppressive agents as cyclosporine and treatment of underlying systemic disease^9,10.

Key diagnostic differences listed in table below (table 2)^5,6,9,13

Table 2: key diagnostic differences between nf and nnd

Pathogenesis, sweet syndrome, neutrophilic eccrine hidradenitis, and behçet disease. J am acad dermatol 2018;79(6):987-1006.
6. sanchez im, lowenstein s: johnson ka. Clinical features of neutrophilic dermatosis variants resembling necrotizing fasciitis. Jama dermatol 2019;155:79-84.
7. wong ch, yam akt, tan abh. Approach to debridement in necrotizing fasciitis. Am j surg 2008;196(3):19-24.
8. Rahman s, daveluy s. Pathergy test. Treasure island (fl). Statpearls publishing, 2022.
9. kroshinsky d, alloo a, rothschild b. Necrotizing sweet syndrome: a new variant of neutrophilic dermatosis mimicking necrotizing fasciitis. J am acad dermatol 2012;67(5):945-954
10. gowda a, christensen l, polly s. Necrotizing neutrophilic dermatosis: a diagnostic challenge with a need for multi-disciplinary recognition, a case report. Annals of medicine and surgery, 2020; 57:299-302.
11. allaw f, wehbe s, kanj ss. Necrotizing fasciitis: an update on epidemiology, diagnostic methods, and treatment. Curr opin infect dis, 2024; 37:105-111.
12. su wp, liu hn. Diagnostic criteria for sweet's syndrome. Cutis, 1986; 37:167-174.
13. misiakos e, bagias g, patapis p. Current concepts in the management of necrotizing fasciitis. Frontiers in surgery, 2014; 1: 36.