Extensive Purpura and Necrosis of the Leg

The Diagnosis: Disseminated Mucormycosis

Histopathologic examination of a 6-mm punch biopsy of the edge of the lesion revealed numerous intravascular, broad, nonseptate hyphae in the deep vessels and perivascular dermis that stained bright red with periodic acid-Schiff (Figure). Acid-fast bacilli and Gram stains were negative. Tissue culture grew Rhizopus species. Given the patient's overall poor prognosis, her family decided to pursue hospice care following this diagnosis.

A and B, Disseminated mucormycosis. Numerous intravascular broad nonseptate hyphae in the deep vessels and perivascular dermis that stained bright red with periodic acid–Schiff (original magnifications ×30).

Mucormycosis (formerly zygomycosis) refers to infections from a variety of genera of fungi, most commonly Mucor and Rhizopus, that cause infections primarily in immunocompromised individuals.¹ Mucormycosis infections are characterized by tissue necrosis that results from invasion of the vasculature and subsequent thrombosis. The typical presentation of cutaneous mucormycosis is a necrotic eschar accompanied by surrounding erythema and induration.² Diagnosis is based on clinical suspicion, requiring additional testing with skin biopsy and tissue cultures for confirmation.

Cutaneous infection is the third most common presentation of mucormycosis, following rhinocerebral and pulmonary involvement.¹ Although rhinocerebral and pulmonary infections normally are caused by inhalation of spores, cutaneous mucormycosis typically is caused by local inoculation, often following skin trauma.² The skin is the most common location of iatrogenic mucormycosis, often from skin injury related to surgery, catheters, and adhesive tape.³ Most patients with cutaneous mucormycosis have underlying conditions such as hematologic malignancies, diabetes mellitus, or immunosuppression.¹ However, outbreaks have occurred in immunocompetent patients following natural disasters.⁴ Cutaneous mucormycosis disseminates in 13% to 20% of cases in which mortality rates typically exceed 90%.¹

Treatment consists of prompt surgical debridement and antifungal agents such as amphotericin B, posaconazole, and isavuconazonium sulfate.¹ Our patient had multiple risk factors for infection, including hematopoietic stem cell transplantation, prolonged neutropenia, and treatment with eculizumab, a monoclonal antibody against C5 that blocks the terminal complement cascade. Eculizumab has been associated with increased risk for meningococcemia,⁵ but the association with mucormycosis is rare. We highlight the importance of recognizing and promptly diagnosing cutaneous mucormycosis given the difficulty of treating this disease and its poor prognosis.

Disseminated aspergillosis demonstrates septate rather than nonseptate hyphae on biopsy. Disseminated intravascular coagulation and purpura fulminans may be associated with thrombocytopenia but demonstrate thrombotic microangiopathy on biopsy. Pyoderma gangrenosum demonstrates neutrophilic infiltrate on biopsy.