Secondary immunodeficiency (SID)
Introduction
What are Secondary immunodeficiencies?
SIDs, also known as acquired immunodeficiencies are caused by external factors, rather than being caused by a hereditary or intrinsic defect.
Estimated to be 30 times more common than PIDs.
Causes
SIDs arise from various factors that weaken the immune system. SID may occur when the immune system is compromised by external factors such as malnutrition, treatments for other diseases or chronic infections1.
Causes of SID include:
- Medications - many newly introduced therapies suppress the immune system. SID as a result of these immunosuppressants is increasing in frequency
- Other diseases or disorders - many diseases can impair immune function including certain blood or bone marrow cancers such as Leukaemia, Lymphoma, and Multiple Myeloma, as well as chronic infections with the most common cause of SID being HIV
- Ageing – can play a role in the development of SID
- Nutritional or metabolic factors – such as diabetes or alcoholism
- Surgery or trauma - could remove or damage essential parts of the immune system, or immune modulatory drugs may be required to minimise the risk of transplant rejection
Examples of SIDs
Possible manifestations of SID:
SID may manifest as an antibody deficiency, which can mimic any of the primary antibody deficiencies. Vaccine response assessment may be used to determine whether these patients are able to mount a response to specific protein or polysaccharide vaccinations. Prophylactic antibiotics and immunoglobulin replacement therapy may be required in some patients.
It may also present as neutropenia. Low neutrophil counts can be caused by immunosuppression or other medical treatments. Therapy may be changed and if not possible, prophylactic antibiotics and antifungals may be required or a neutrophil stimulating treatment.
It may also present as a T cell deficiency. Patients with reduced T cells may suffer from multiple infections. If the underlying cause of this immunodeficiency cannot be removed, then the patient may be treated with antiviral, antifungal, or antibiotic therapies.
Prevalence
As there are many different possible causes, epidemiological data is very difficult to obtain. These patients may be found in a number of different situations, or clinics, and may have a number of other problems that clinicians are trying to manage.
Diagnosis
What are the current strategies for the investigation of secondary immunodeficiency?
An algorithm was proposed for the identification of secondary antibody deficiency and provides guidance for treatment options and monitoring.2
Treatment
Treatment or management of the underlying cause of SID will often lead to improvement in symptoms, as the immune system is able to recover. However, sometimes this is not feasible, and treatment for the immunodeficiency may be required in order to prevent serious infections.
References
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