Concurrent Sweet Syndrome and Erythema Nodosum: Two Sides of the Same Coin?

A 37-year-old woman presented to the dermatology department with a two-week history of fever, daily temperature peaks of up to 39°C, and immobilizing joint pain, along with a one-week history of erythematous skin lesions. She reported previous mild gastrointestinal and respiratory symptoms. During the physical examination, multiple tender succulent erythematous plaques were observed on her upper trunk and arms ( gure 1A, B). Additionally, painful erythematous indurated nodules were present bilaterally on the pretibial area ( gure 1C), consistent with erythema nodosum (EN). Laboratory tests revealed leukocytosis at 9,800/μL (reference range: 4,370-9,680/μL) with relative neutrophilia at 76.7% (reference range: 42.5-73.2%), elevated C-reactive protein (CRP) at 4.66 mg/dL (reference range: <0.5 mg/dL), and positive serology for Mycoplasma pneumoniae (IgG, IgA, and IgM) as well as Yersinia (IgG and IgA). Treatment with clarithromycine was given for seven days. Monoclonal gammopathy was ruled out based on serum protein electrophoresis. A lesional skin biopsy from the right scapula showed a perivascularly accentuated neutrophil-rich in ammatory in ltrate ( gure 1D) and oedema of the papillary dermis, consistent with Sweet syndrome (SS), associated with a recent Mycoplasma or Yersinia infection. Treatment with oral prednisolone (1 mg/kg/day) was initiated, and the patient showed a dramatic response within one week. Prednisolone was therefore tapered off within one month. Upon treatment, she did not experience any more febrile episodes, and her arthralgia and skin lesions rapidly resolved. SS is a rare skin disease rst described in 1964 as acute febrile neutrophilic dermatosis [1]. It is characterized by tender erythematous plaques, fever, arthralgia, leukocytosis with neutrophilia and conjunctivitis. Its distinctive histological feature is a neutrophilic dermal in ltrate with the absence of leukocytoclastic vasculitis. However, vasculitis has been described in rare cases [2]. On the other hand, EN manifests as painful indurated erythematous nodules predominantly on the pretibial area. Septal panniculitis accompanied by a mixed neutrophilic and lymphocytic in ltrate with the absence of vasculitis are histological hallmarks of EN. Although the simultaneous occurrence of both SS and EN is rare, a few cases have been described [3-5]. Both are reactive dermatoses with overlaying clinical features such as fever, arthralgia, and elevated CRP that may be associated with underlying conditions such as upper respiratory tract infection, in ammatory bowel disease, Behçet’s disease, malignancies [6], and sarcoidosis. Moreover, both SS and EN respond to the same treatments and manifest with common histopathological features such as a predominantly neutrophilic in ltrate [4]. Although EN itself is not a neutrophilic dermatosis (ND), both are reactive processes to common stimuli, and associations with other NDs such as pyoderma gangraenosum have been described [7]. Whereas patients usually only develop one distinctive cutaneous reaction pattern to such stimuli, these concurrences and shared associated diseases suggest a mutual pathomechanism, although the causative initiating event remains unknown in both diseases [8]. Similar cytokine patterns may manifest in the dermis in SS, in the subcutaneous tissue in EN, and in both in some rare cases, such as the case described here. ■