Acute Febrile Neutrophilic Dermatosis (Sweet Syndrome) Workup

Updated: Jun 02, 2020
  • Author: Yoon-Soo (Cindy) Bae, MD; Chief Editor: William D James, MD  more...
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Laboratory Studies

The diagnosis of Sweet syndrome (acute febrile neutrophilic dermatosis) includes histopathologic evidence per the criteria mentioned in Physical Examination. Clinicopathologic correlation is important because bowel bypass syndrome may present with skin lesions with an identical histologic picture. [2, 4, 82]

Although laboratory tests can be nonspecific, the tests described below can be helpful in the diagnosis and further workup for Sweet syndrome, especially when investigating for an underlying cause.

A complete blood cell (CBC) count with differential must be ordered to detect for minor criteria and to screen for hematologic disorder or malignancy. Neutrophilia is typically present, but the absence of neutrophilia in a patient who is neutropenic does not rule out Sweet syndrome. Anemia and thrombocytopenia are common in patients with underlying malignancy.

Abnormalities in the CBC count should prompt consideration of bone marrow biopsy. [2, 81, 82]

Erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP) levels may be elevated. One report notes that ESR is elevated in more than 90% of cases. [82] However, both of these findings are nonspecific manifestations of inflammation. [2, 82]

Urinalysis may show proteinuria and/or hematuria. [8]

Hepatic panel may show nonspecific elevation of hepatic enzymes. [35]

Antineutrophilic cytoplasmic antibodies (ANCAs) have been described but not consistently found in all patients with Sweet syndrome. [109]

Lesions should be cultured for bacteria, fungi, and mycobacteria to rule out infection. [2]


Imaging Studies

A chest radiograph should be obtained if pulmonary symptoms of Sweet syndrome (acute febrile neutrophilic dermatosis) are present because this form is responsive to systemic corticosteroids. [4]

Sweet syndrome is the presenting sign of malignancy in approximately two thirds of the cases of malignancy-associated Sweet syndrome. [4] For this reason, the presence of ulcerative lesions, oral lesions, abnormal platelet counts, or anemia should prompt investigation for an underlying malignancy. [8] Some authors recommend a complete systemic evaluation in all patients with Sweet syndrome. [28] If an underlying malignancy is suspected, the appropriate imaging modality should be used for early detection and treatment. [2]

2-[Fluorine 18]-Fluoro-2-deoxy-D-glucose (FDG) positron-emission tomography (PET) is especially useful in evaluating myeloproliferative disorders, but it can also be helpful in assessing some solid tumors and has successfully depicted early malignancies. [110]



Skin biopsy should be performed to confirm the diagnosis of Sweet syndrome (acute febrile neutrophilic dermatosis) per the major criteria listed in Physical Examination. [2]

Bone marrow aspiration is indicated if the CBC count is abnormal, and it should be considered in all cases of atypical bullous or ulcerative Sweet syndrome to detect for myelodysplastic disease. [88]

Age-appropriate cancer screening and evaluation for inflammatory bowel disease are indicated if no other underlying cause is found, especially in patients with bullous or ulcerative lesions. [2]


Histologic Findings

The classic histopathologic pattern of Sweet syndrome (acute febrile neutrophilic dermatosis) consists of a dense, diffuse neutrophilic infiltrate in the reticular dermis. Leukocytoclastic nuclear debris is typically present interstitially, and massive papillary dermal edema is common. True vasculitic changes (expansion of postcapillary venule wall with fibrin deposition) are absent. Eosinophils and lymphocytes are present in some instances, but neutrophils usually predominate. [2]

The epidermis usually is spared, although nonspecific findings such as spongiosis and subcorneal pustule formation can be seen. [82]

Results of direct immunofluorescence testing are noncontributory. In rare cases, the inflammation extends to involve the subcutis. In essentially all instances, cases with subcutaneous involvement also show extensive involvement of the reticular dermis. [82]

Histiocytoid Sweet syndrome is a variant that has been described and includes histiocytoid cells, which are immature myeloid cells commonly mistaken as histiocytes. The most important differential diagnosis for this variant is leukemia cutis. [111] Other histologic variants include lymphocytic, subcutaneous, and crytococcoid types. [86]