Question: What is (are) Hypocomplementemic urticarial vasculitis syndrome ?
Answer: Hypocomplementemic urticarial vasculitis (HUV) is a rare form of cutaneous small-vessel vasculitis characterized by recurrent episodes of urticaria and painful, tender, burning or itchy skin lesions, often associated with extracutaneous involvement but usually with no significant peripheral nerve damage. Patients with this condition are likely to have systemic involvement, including angioedema, arthralgias, pulmonary disease, abdominal or chest pain, fever, renal disease, and episcleritis. Hypocomplementemic urticarial vasculitis is thought be an autoimmune response involving a specific region of complement 1 (C1). It can present as or precede a syndrome that includes obstructive pulmonary disease , uveitis, systemic lupus erythematous (SLE), Sjgren's syndrome, or cryoglobulinemia (which is closely linked with hepatitis B or hepatitis C virus infection). Some cases of hypocomplementemic urticarial vasculitis respond to therapies commonly used for the treatment of SLE, including low-dose prednisone, hydroxychloroquine, dapsone, or other immunomodulatory agents.
Source: GARD

Question: How to diagnose Hypocomplementemic urticarial vasculitis syndrome ?
Answer: How is hypocomplementemic urticarial vasculitis (HUV) diagnosed? What kind of tests are required? A diagnosis of hypocomplementemic urticarial vasculitis (HUV) syndrome is supported by findings from varied tests, such as skin biopsy, blood tests, physical and eye examinations, and urinalysis and kidney imaging studies (when glomerulonephritis is suspected). People with HUV syndrome have hives (urticaria) for at least six months and low levels of proteins (complement) in the blood. Complement levels can be determined through a blood test. Click here to visit the American Association for Clinical Chemistry's Web site Lab Tests Online to learn more about this test. In addition to these major criteria, people with HUV syndrome must also have at least two of the following minor criteria: Inflammation in the small veins of the dermis (diagnosed by biopsy) Joint pain or arthritis Mild glomerulonephritis Inflammation in the eye (uvea or episclera) Recurrent abdominal pain The presence of anti-C1q antibodies (this test is not widely available) Some people have urticarial vasculitis and low complement levels (hypocomplementemia), but do not meet diagnostic criteria for HUV syndrome. These individuals may be diagnosed as having HUV (where symptoms are limited to the skin), versus HUV syndrome. Differential diagnoses for HUV syndrome include, Schnitzler's syndrome, Cogan's syndrome, and Muckle-Wells syndrome.
Source: GARD