Currently unknown. (Some patients with somatic NLRP3 mutations.) 
Affects all races, but most cases are in Europe.  More men than women are affected.
Unknown. Over 150 known cases, mostly in Europe. 
Timing of symptoms:
12-36 hours. Rash is present first. Intermittent fevers often occur separately from the rash. 
Age of onset:
Most cases start in middle age, at over 35-50 years old. The youngest patient was 13 yrs old. Symptoms start with the rash. 
Maculopapular rash and plaques (sometimes itchy) on the chest and limbs. Dermis has neutrophillic infiltrate. Dermographism. 
Intermittent fevers can rise >40°C. Chills are uncommon. Fatigue and headaches are common with fevers. Temperature changes (weather), stress and/or exercise can trigger flares. 
Not noted. 
Not noted. 
GI symptoms are uncommon. Hepatomegaly, splenomegaly or hepatosplenomegaly is common. 
<20% with lymphoma, IgM myeloma, or Waldenströms macroglobulinemia (aka lymphoplasmacytic lymphoma). >45% with lymphadenopathy. Splenomegaly. 
Joints bones muscles cartilage:
80% have muscle, bone and/or joint pain, or arthritis. Bone pain is most common in the iliac and tibia. <40% have bone lesions. Some with osteocondensation and sclerotic bone marrow involvement in the legs. 
Vasculitis noted in 20% of patients. 
A few patients have developed secondary amyloidosis. 
Monoclonal IgM and/or IgG gammopathy. High: ESR, CRP. Leukocytosis. Complement normal to elevated. 50% with inflammatory anemia. 
Schnitzler syndrome, Schnitzler's, Schnitzler's syndrome, Schnitzlers syndrome, Maculopapular, plaques, dermographism, urticaria, periodic fever, periodic fevers, recurrent fevers, fatigue, headache, IgM gammopathy, IgG gammopathy, IgM, IgG, anemia, intermittent fever, fever rash, adult onset rash, joint pain, muscle pain, bone pain, bone lesions, amyloidosis, complement, vasculitis, lymphoma, IgM myeloma, Waldenströms macroglobulinemia (aka lymphoplasmacytic lymphoma, lymphadenopathy, hepatomegaly, splenomegaly, hepatosplenomegaly, intermittent fever, rash, urticarial rash, adult onset, arthritis, enlarged liver, enlarged spleen,enlarged liver and spleen, pain, amyloid, SAA
Pr Xavier Kyndt (CH Valenciennes) Schnitzler Syndrome image 6/8. Cri-net.com
There are no known genetic tests yet for Schnitzler's Syndrome. There is a clinical trial to find the genetic causes for Schnitzler's syndrome in France that is open for enrollment.
UCL Patient information for Schnitzler's syndrome to print out.
Our Autoinflammatory Alliance website Schnitzler's Syndrome page.