Disseminated cutaneous mucormycosis resembling multiple panniculitis

Mucorales are ruderal fungi; human infections involving these fungi tend to cause significant morbidity and mortality in susceptible patient populations. Cutaneous mucormycosis has variable clinical presentations resulting from angioinvasion, leading to skin necrosis with eschars.1 The rapid extension of the lesions and the destructive character of the disease require swift diagnosis and appropriate antifungal therapy. When mistaken for a non-fungal disorder, therapy may target the reduction of inflammation through the administration of corticosteroids, which further promotes the mucoralean infection. Herein, we report a case of disseminated cutaneous mucormycosis presenting with multiple nodules at an early stage, which was misdiagnosed as panniculitis. A 65-year-old retired male patient presented to the outpatient department due to the sudden onset of dozens of red egg-sized painful nodules on the trunk and both lower limbs (Figure 1a–c) accompanied by occasional fever for 32 days, with no improvement upon the application of clindamycin. Twenty-four days before presentation, he was prescribed methylprednisolone 40 mg/day intravenously (IV) for 7 days at a local hospital, with a provisional diagnosis of possible panniculitis. However, the lesions gradually protruded, and some ruptured with purulent secretion in the center. Two years earlier, he was diagnosed with eosinophilic dermatosis, and oral therapy was initiated with prednisone at 30 mg/day, with a decrease to 25 mg/day orally before the onset of the disease. Magnetic resonance imaging (MRI) revealed multiple ellipsoidal masses with relatively clear boundaries, ranging from 0.8 to 4.4 cm in diameter, in the subcutaneous tissues of the chest and abdomen. No evidence of deep soft tissue or muscular structure infection was observed (Figure 2c). Computed tomography (CT) scans of the brain, thorax, abdomen, and pelvis showed no apparent foci of infection. Laboratory test results were negative for human immunodeficiency virus (HIV). Through exudate microscopy (Figure 2a), histopathological examination (Figure 2b), and a real-time polymerase chain reaction (PCR) test of skin tissue (Figure 2d), cutaneous mucormycosis caused by Rhizopus arrhizus was diagnosed. Specimen culture was negative for mucorales. The patient was treated with thrice-weekly hemodialysis and oral posaconazole for acute renal insufficiency. Unfortunately, he refused to take posaconazole due to anorexia and died 3 months later. Cutaneous mucoralean infection is mostly associated with a breach of the skin barrier caused by burns, traffic accidents, or other types of deep trauma.2 The infection is often characterized by a severe course. In patients with underlying immune or metabolic disorders, the portal of entry may remain unclear.1 In association with diabetes mellitus and hematological malignancies,2 long-term corticosteroid treatment is an additional risk factor for mucormycosis,3 but given the wide application of immunodepressives, is much less obviously linked to mucoralean infection. For the definitive diagnosis of invasive mold infection, a fungal organism must be identified through histopathology, sterile culture, or the amplification of fungal DNA via PCR in tissue samples. It is not advisable to excessively grind skin biopsy specimens suspected of containing mucormycosis, as this may negatively affect the culture's positivity rate. In instances where cultures yield negative results, the significance of real-time PCR diagnosis should be thoroughly evaluated, considering its 62% sensitivity for detecting mucorales in formalin-fixed, paraffin-embedded tissue samples. Disseminated cutaneous mucormycosis may manifest as panniculitis or erythema nodosum in a few instances, with two cases showing multiple subcutaneous nodules at different sites.4, 5 This rare presentation resembles the more common chronic subcutaneous inflammation of panniculitis. Corticosteroids should be avoided when infection-related panniculitis is a concern to prevent aggravating the condition. In the present case, the patient denied a history of trauma or injection and did not have accompanying deep infection of soft tissue or internal organs. In conclusion, disseminated cutaneous mucormycosis should be considered as a differential diagnosis when a patient with long-term corticosteroid treatment develops multiple erythema nodosum-like lesions with panniculitis. All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by Xingye Meng, Xiao Liu, and Tianwei Liang. The first draft of the manuscript was written by Tianwei Liang and supervised by G. Sybren de Hoog, Yinggai Song, and Ruoyu Li. All authors commented on the previous versions of the manuscript and approved the final manuscript. We thank the patient's family for providing written informed consent to the publication of the patient's case details and images. Informed consent was obtained from the family of the patient included in the study. The family agreed the authors could use and publish the patient's disease-related data and photographs with the omission of personal information. The data used or analyzed in the current study are available from the corresponding authors upon reasonable request.