Keeping watch on immune system


Keeping watch on immune system

Charles Essex
The over-65s and children under five years have a disproportionate number of consultations with the GP relative to their proportion of the practice population. Young children most commonly present with infections and some children seem to have a particular body system most likely to be affected; “When he gets a cold it always goes to his chest [or ears, throat, etc].”

Most primary school teachers will tell you they rarely have a full class because one child, or more, is off with an infection, yet, by secondary school age, absence due to ill health is much less common. It is part of the maturing of the immune system as we grow. So, when should we think of an immune problem in the face of a normal developmental process?

Immunodeficiency was first described in 1952 but, over 50 years later, the diagnosis is delayed on average five years from presentation. The majority is seen initially in paediatric, ENT and chest clinics, but 60 per cent of patients do not have the diagnosis made in the first three hospital visits. Immunodeficiency causes children and adults to have infections that recur frequently and are usually hard to cure. The acronym SPUR – serious, persistent, unusual, recurrent – applied to infections will suggest if a patient’s immune function should be tested.

Red flag signs would include two episodes of meningitis, which would be both serious and recurrent and may suggest a deficiency of the complement system. Opportunistic infection such as persistent thrush, which is unusual, would suggest there may be a T-cell deficiency. Deep abscesses such as a liver abscess, which would be unusual, suggest investigation to look for a neutrophil deficiency.

The five types of immunoglobulin are IgG, IgM, IgD, IgA and IgE. IgG and IgM are part of the systemic immunity, with IgM production being triggered first in response to an infection followed by IgG, the latter acting as the immunological memory. IgA is part of the mucosal immune system.

Splenomegaly, abnormal white cell count, chronic diarrhoea and chronic sinusitis, while not sensitive as screening tools, should at least make one think of immunodeficiency. These features, together with failure to thrive, developmental difficulties, etc, particularly in a child whose parents are consanguineous, would also warrant a full investigation.

Investigations include a full blood count and a differential. Frequently, apart from the neutrophil count, the differential blood count is often overlooked. The lymphocyte count in children under two years should be above 2.7. A lymphocytopenia in a child under two years should make one think of severe combined immunodeficiency (SCID). Requesting the immunoglobulin count – quite a cheap test – will show up as three main subgroups, IgG, IgM and IgA.

Specific antibody levels can also be requested for vaccine-related antibody levels, in particular tetanus, diphtheria and pneumococcus. These act as a guide to the overall immune function. The child can be given these vaccines, even if they have had them before, and the antibody levels can be tested post vaccination. Although ideally one should test before and after antibody levels, on a practical basis, one often just takes a post immunisation blood test. Even though two years is quoted for a minimum age for a response to a polysaccharide vaccine, children may not respond to the Pneumovax immunisation even up to the age of five years.

Lastly, do not forget the HIV test. Although there is still concern about approaching the parents to discuss this because of the stigma, if it is not considered, it will never be discovered as a cause of some children’s recurrent infections and immune problems.

Charles Essex is a consultant neurodevelopmental paediatrician based in Coventry, UK.

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