Sweet's syndrome
Synonyms and keywords: Acute febrile neutrophilic dermatosis.

# Overview
Sweet's syndrome, or acute febrile neutrophilic dermatosis, is a condition characterized by the sudden onset of fever, leukocytosis, and tender, erythematous, well-demarcated papules and plaques which show dense neutrophilic infiltrates on histologic examination.

# Historical Perspective
Sweet, in 1964, described a disease with four features: fever; leukocytosis; acute, tender, red plaques; and a papillary dermal infiltrate of neutrophils. This led to the name acute febrile neutrophilic dermatosis. Larger series of patients showed that fever and neutrophilia are not consistently present. The diagnosis is based on the two constant features, a typical eruption and the characteristic histologic features; thus the eponym Sweet's syndrome (SS) is used.

# Pathophysiology
Sweet's syndrome can be classified based upon the clinical setting in which it occurs: classical or idiopathic Sweet's syndrome, malignancy-associated Sweet's syndrome, and drug-induced Sweet's syndrome.
SS is a reactive phenomenon and should be considered a cutaneous marker of systemic disease. Careful systemic evaluation is indicated, especially when cutaneous lesions are severe or hematologic values are abnormal. Approximately 20% of cases are associated with malignancy, predominantly hematological, especially acute myelogenous leukemia. An underlying condition (streptococcal infection, inflammatory bowel disease, nonlymphocytic leukemia and other hematologic malignancies, solid tumors, pregnancy) is found in up to 50% of cases. Attacks of SS may precede the hematologic diagnosis by 3 months to 6 years, so that close evaluation of patients in the idiopathic group is required.
There is now good evidence that treatment with hematopoietic growth factors, including granulocyte colony-stimulating factor, which is used to treat acute myelogenous leukemia, and granulocyte-macrophage colony-stimulating factor, can cause Sweet's syndrome. Lesions typically occur when the patient has leukocytosis and neutrophilia but not when the patient is neutropenic. However, G-CSF may cause SS in neutropenic patients because of the induction of stem cell proliferation, the differentiation of neutrophils, and the prolongation of neutrophil survival.

# Associated Diseases
Although it may occur in the absence of other known disease, Sweet's syndrome is often associated with hematologic disease (including leukemia), and immunologic disease (rheumatoid arthritis, inflammatory bowel disease).

# Diagnosis
Acute, tender, erythematous plaques, nodes, pseudovesicles and, occasionally, blisters with an annular or arciform pattern occur on the head, neck, legs, and arms, particularly the back of the hands and fingers.  The trunk is rarely involved. Fever (50%); arthralgia or arthritis (62%); eye involvement, most frequently conjunctivitis or iridocyclitis (38%); and oral aphthae (13%) are associated features. Differential diagnosis includes erythema multiforme, erythema nodosum, adverse drug reaction, and urticaria. Recurrences are common and affect up to one third of patients.

# Physical examination

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# Laboratory Studies
Studies show a moderate neutrophilia (less than 50%), elevated ESR (greater than 30 mm/hr) (90%), and a slight increase in alkaline phosphatase (83%). Skin biopsy shows a papillary and mid-dermal mixed infiltrate of polymorphonuclear leukocytes with nuclear fragmentation and histiocytic cells. The infiltrate is predominantly perivascular with endothelial-cell swelling in some vessels, but vasculitic changes (thrombosis; deposition of fibrin, complement, or immunoglobulins within the vessel walls; red blood cell extravasation;inflammatory infiltration of vascular walls) are absent in early lesions.
Vasculitis occurs secondary to noxious products released from neutrophils. Blood vessels in lesions of longer duration are more likely to develop vasculitis than those of shorter duration because of prolonged exposure to noxious metabolites. Therefore, vasculitis does not exclude a diagnosis of Sweet's syndrome

# Treatment
Systemic corticosteroids (prednisone 0.5 to 1.5 mg/kg of body weight per day) produce rapid improvement and are the gold standard for treatment. The temperature, WBC count, and eruption improve within 72 hours. The skin lesions clear within 3 to 9 days. Abnormal laboratory values rapidly return to normal. There are, however, frequent recurrences. Corticosteroids are tapered within 2 to 6 weeks to zero. Resolution of the eruption is occasionally followed by milia and scarring. The disease clears spontaneously in some patients. Topical and/or intralesional corticosteroids may be effective as either monotherapy or adjuvant therapy.
Oral potassium iodide or colchicine may induce rapid resolution. Patients who have a potential systemic infection or in whom corticosteroids are contraindicated can use these agents as a first-line therapy.
In one study, indomethacin, 150 mg per day, was given for the first week, and 100 mg per day was given for 2 additional weeks. Seventeen of 18 patients had a good initial response; fever and arthralgias were markedly attenuated within 48 hours, and eruptions cleared between 7 and 14 days. Patients whose cutaneous lesions continued to develop were successfully treated with prednisone (1 mg/kg per day). No patient had a relapse after discontinuation of indomethacin.
Other alternatives to corticosteroid treatment include dapsone, doxycycline, clofazimine, and cyclosporine. All of these drugs influence migration and other functions of neutrophils.