Common variable immunodeficiency

Common Variable Immunodeficiency, commonly known as CVID, is a group of 20-30 Primary Immunodeficiencies (PIDs) which have a common set of symptoms but with different underlying causes.

CVID's underlying causes are different, but the result of these are that the patient doesn't produce sufficient antibodies in response to exposure to pathogens. As a result, the patient's immune system fails to protect them against common bacterial and viral (and occassionally parasitic and protozoal) infections. The net result is that the patient is prone to illness. CVID has a prevalence is about 1:50,000, meaning that approximately 1,200 patients in the UK probably have this diagnosis.

Symptoms of CVID are:

• hypogammglobulinaemia, or low levels of Immunoglobulin G (IgG)
• many patients have low levels of Immunogloblin A (IgA) and Immunoglobulin M (IgM)
• polyarthritis, or joint pain, spread across most joints, but specifically fingers, wrists, elbows, toes, ankles and knees
• repeated incidence of infections which respond to antibiotics and antivirals, specifically: upper respiratory tract infections (URTIs), sinusitis, tonsilitis, epiglotitis, dermatological abcesses/boils (often, but not exclusively, facial and axillary), pneumonia, bronchitis, pleurisy, stomach/intestinal infections, colds, influenza, shingles, conjunctivitis
• diarrhoea (often arises as a result of "minor" intestinal infections, including protozoal and parasitic infections)
• bronchiectasis (lung tissue damage as a result of repeated chest infections) leading to shortness of breath
• poor titer levels in response to vaccination (ie: doctor gives the patient a pneumonia vaccine (Pneumovax II), and two weeks later tests to see what levels of pneumonia antibodies are in the blood stream). This is often carried out on polysaccharide and non-polysaccharide coated pathogens (eg: pneumonia and tetanus)
• children may show a "failure to thrive" - they may be underweight and underdeveloped compared with 'normal' peers
• patients may lose weight

It is not unusual for a person with CVID to treated as a hypochondric, and they will often have spent significant amounts of time off sick, whether from school or work. Diagnosis normally takes in excess of two years, and diagnosis is often made in the second or third decade of life after referral to an immunologist.

Because CVID is a catch-all diagnosis, which encompasses a number of as-yet undifferentiated disorders, the cause of each specific disorder is different so one can't identify a single common theme. Some cases appear to be genetic, like Severe Combined Immunodeficiency (SCID) - or boy in a bubble disease, some appear to be environmental in some way, some may be pathogenic (with Epstein-Barr Virus implicated by some informal research). Most of the diagnoses are probably a combination of genetic predisposition along with a pathogenic or ecogenic trigger.

Research is currently focussing on genetic analysis, and in differentiating between the various different disorders in order to allow a cure to be developed. Cures are likely to be genetic in nature, repairing faulty genes and allowing the individual to start producing antibodies. Key research in the UK is funded by the Primary Immunodeficiency Association (PiA), and funding is raised through the annual Jeans for Genes campaign.

Treatment usually consists of immunoglobulin therapy, either Intravenous Immunoglobulin G (IVIG), Sub-Cutaneous Immunoglobulin G (SCIG) or (less frequently) Intramuscular Immunglobulin (IMIG). This isn't a cure, but does help to ensure the patient has "normal" levels of antibodies, which helps to prevent recurrent infections. IG therapy may be inappropriate if the patient has anti-IgA antibodies.

Few CVID patients have bad clinical reactions to IG therapies, but reactions may include:

• anaphylactic shock (very rare)
• hives (rare)
• headache (relatively common, relieved by an antihistamine and paracetamol/acetaminophen)

Patients should not receive therapy if they are fighting an active infection as this increases the risk of reaction.

Reactions can be minimised by taking an antihistamine and some paracetamol/acetaminophen prior to treatment; patients should also be thoroughly hydrated and continue to drink water before, after and during treatment (if possible).