Sweet's syndrome :

Acute febrile neutrophilic dermatosis, also termed Sweet syndrome, is a reactive process characterized by the abrupt onset of tender, red-to-purple papules, and nodules that coalesce to form plaques.

Pathophysiology : It is a reactive process (a hypersensitivity reaction) that occurs in response to systemic factors, such as hematologic disease, infection, inflammation, vaccination, or drug exposure.

Epidemiology : Typically, women with acute febrile neutrophilic dermatosis (Sweet syndrome) are aged 30-50 years.However, cases in neonates as young as 5 days have been described.

Clinical presentation :
Fever can precede the skin disease by several days to weeks; however, it may also occur simultaneously. The crop of plaques or nodules in the classic form often appears abruptly and may persist for weeks or several months (days to weeks) if untreated.

Many patients report a febrile upper respiratory tract infection, tonsillitis, or flulike syndrome weeks prior to onset of skin lesions. Vaccination or a gastrointestinal tract infection may also precede the eruption.Headache, malaise, and arthralgias are common.