Diagnosis
Blood tests show a high concentration of specific gamma-globulins (monoclonal gammopathy) of the IgM type. It almost always has light chains of the κ-type. A variant in which IgG is raised has been described, which appears to be ten times as rare. The immunoglobulins may show up in the urine as Bence Jones proteins. Signs of inflammation are often present: these include an increased white blood cell count (leukocytosis) and a raised erythrocyte sedimentation rate and C-reactive protein. There can be anemia of chronic disease. Bone abnormalities can be seen on radiological imaging (often increased density or osteosclerosis) or biopsy.
Because it is such a rare condition (less than 100 cases reported in the literature worldwide before 2008), it is important to rule out other conditions which can cause periodic fevers, paraproteins or chronic hives. These include (and are not limited to) auto-immune or -inflammatory disorders such as adult-onset Still's disease, angioedema, hematological disorders such as lymphoma or monoclonal gammopathy of undetermined significance, other causes of hives, cryoglobulinemia, mastocytosis, chronic neonatal onset multisystem inflammatory disease or Muckle-Wells syndrome. It is however possible to have more than one rare condition as seen by a patient with Schnitzler's syndrome and cold induced urticaria.
Read more about this topic: Schnitzler Syndrome