To the Editor:
Necrotizing myositis (NM) is an exceedingly rare necrotizing soft-tissue infection (NSTI) that is characterized by skeletal muscle involvement. β -Hemolytic streptococci, such as Streptococcus pyogenes , are the most common causative organisms. The overall prevalence and incidence of NM is unknown. A review of the literature by Adams et al 2 identified only 21 cases between 1900 and 1985.
Timely treatment of this infection leads to improved outcomes, but diagnosis can be challenging due to the ambiguous presentation of NM and lack of specific cutaneous changes.3 Clinical manifestations including bullae, blisters, vesicles, and petechiae become more prominent as infection progresses.4 If NM is suspected due to cutaneous manifestations, it is imperative that the underlying cause be identified; for example, NM must be distinguished from the overlapping presentation of pyoderma gangrenosum (PG). Because NM has nearly 100% mortality without prompt surgical intervention, early identification is critical.5 Herein, we report a case of NM that illustrates the correlation of clinical, histological, and imaging findings required to diagnose this potentially fatal infection.
An 80-year-old man presented to the emergency department with worsening pain, edema, and spreading redness of the right wrist over the last 5 weeks. He had a history of atopic dermatitis that was refractory to topical steroids and methotrexate; he was dependent on an oral steroid (prednisone 30 mg/d) for symptom control. The patient reported minor trauma to the area after performing home renovations. He received numerous rounds of oral antibiotics as an outpatient for presumed cellulitis and reported he was “getting better” but that the signs and symptoms of the condition grew worse after outpatient arthrocentesis. Dermatology was consulted to evaluate for a necrotizing neutrophilic dermatosis such as PG.
At the current presentation, the patient was tachycardic and afebrile (temperature, 98.2 °F [36.8 °C]). Physical examination revealed large, exquisitely tender, ill-defined necrotic ulceration of the right wrist with purulent debris and diffuse edema (Figure 1). Sequential evaluation at 6-hour intervals revealed notably increasing purulence, edema, and tenderness. Interconnected sinus tracts that extended to the fascial plane were observed.
FIGURE 1. Necrotizing myositis of the right hand and forearm with diffuse redness, erythema, and edema surrounding a large necrotic ulceration with purulent debris.
Laboratory workup was notable for a markedly elevated C-reactive protein level of 18.9 mg/dL (reference range, 0–0.8 mg/dL) and an elevated white blood cell count of 19.92×109/L (reference range, 4.5–11.0×109/L). Blood and tissue cultures were positive for methicillin-sensitive Staphylococcus aureus. Computed tomography and magnetic resonance imaging (MRI) prior to biopsy demonstrated findings consistent with extensive subcutaneous and intramuscular areas of loculation and foci of gas (Figure 2). These findings were consistent with intramuscular involvement. A punch biopsy revealed a necrotic epidermis filled with neutrophilic pustules and a dense dermal infiltrate of neutrophilic inflammation consistent with infection (Figure 3).
FIGURE 2. Sagittal view of T1-weighted, postcontrast, fat-saturated magnetic resonance imaging of necrotizing myositis of the wrist, demonstrating rim-enhanced intramuscular abscesses (asterisk), contrast-enhancing erosions of the carpus (arrows), and rim-enhancing tenosynovial fluid (arrowheads).
Emergency surgery was performed with debridement of necrotic tissue and muscle. Postoperatively, he became more clinically stable after being placed on cefazolin through a peripherally inserted central catheter. He underwent 4 additional washouts over the ensuing month, as well as tendon reconstructions, a radial forearm flap, and reverse radial forearm flap reconstruction of the forearm. At the time of publication, there has been no recurrence. The patient’s atopic dermatitis is well controlled on dupilumab and topical fluocinonide alone, with a recent IgA level of 1 g/L and a body surface area measurement of 2%. Dupilumab was started 3 months after surgery.
FIGURE 3. A biopsy specimen of the right wrist revealed a necrotic epidermis with neutrophilic pustules and a dense dermal infiltrate comprised of neutrophils that was characteristic of necrotizing myositis (H&E, original magnification ×100).
Necrotizing myositis is a rare, rapidly progressive infection involving muscle that can manifest as superficial cutaneous involvement. The clinical manifestation of NM is harder to recognize than other NSTIs such as necrotizing fasciitis, likely due to the initial prodromal phase of NM, which consists of nonspecific constitutional symptoms.3 Systemic findings such as tachycardia, fever, hypotension, and shock occur in only 10% to 40% of NM patients.4,5