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Immunology and Allergy Services in Scotland

II: ALLERGY, PRIMARY IMMUNODEFICIENCY AND AUTOIMMUNE DISEASE

Introduction

14 The spectrum of clinical conditions covered in this report falls into three main categories, namely allergy, primary immunodeficiency and autoimmune disease. Although allergic disease forms the vast majority of patient referrals, smaller numbers in other categories require significant input in terms of resources. A brief description of each of these conditions is given below.

Allergy

15 Allergy is a form of exaggerated sensitivity (hypersensitivity) to a substance which is either inhaled, swallowed, injected, or comes in contact with the skin, eyes, or mucous membranes. Doctors use the term allergy to describe situations where hypersensitivity results from heightened (or "altered") reactivity of the immune system in response to external or "foreign" substances.

16 Foreign substances that provoke allergies are called allergens. Examples include grass, weed and tree pollens, substances present in house dust (particularly the house dust mite), fungal spores, animal products, certain food and drugs, and various chemical agents encountered in the home and at work. Patients who develop common allergies such as hayfever are called "atopic". The atopic state runs in families and is genetically transmitted. Atopic individuals produce increased amounts of immunoglobulin E (IgE), a type of antibody which binds particularly avidly to mast cells. These cells are located throughout the body and release histamine and other inflammatory agents when triggered by the allergen. The common atopic conditions are hayfever, eczema, allergic (atopic) asthma and immediate (IgE-mediated) reactions to foods.

17 The clinical spectrum of allergic disease encompasses:

• Seasonal allergic rhinoconjunctivitis

• Perennial rhinoconjunctivitis

• Allergic forms of asthma, including occupational asthma

• Stinging and biting insect allergy

• Drug allergy

• Allergic skin disorders

• Food allergy (e.g. peanuts, shellfish, etc)

• Anaphylaxis (an acute, severe generalised allergic reaction which is a life-threatening condition).

18 Some estimates suggest that between 10 - 30% of the population have a clinical allergic disorder.⁷ Allergic diseases are already a major cause of morbidity and, occasionally, mortality.¹ They are also a major cause of work/school absence and impose a significant economic burden on the NHS.¹ An estimate of the annual cost to the NHS of asthma alone is £750m.⁸

Primary Immunodeficiency

19 This term refers to all those conditions in which immune responses are inadequate as a consequence of primary failure of the immune system or a component thereof rather than being due to another disease or pathological process.

20 Because of the critical role of the immune system as a defence against infection such immunodeficiencies are most often associated with an increased frequency of infection but they may also be complicated by other disorders such as tumours or autoimmune diseases.⁹

21 The primary immunodeficiencies in which immunologists make major contributions to diagnosis, investigation and management can be categorised as being defects of the production and / or function of antibodies (primary antibody deficiency) (see paragraphs 23-25 below), lymphocyte number and function (cellular immunodeficiency), and co-existent antibody and cellular deficiency. Also included in this category are defects of other immune mechanisms such as the complement system.

22 The conditions referred to above are listed in the order of their relative frequency and therefore their contribution to the immunologists' immunodeficiency workload. Primary antibody deficiency is the most common and also the most demanding in terms of use of resources.

23 Primary antibody deficiency syndromes include congenital and acquired defects of antibody production but not those which occur secondary to other diseases, such as myeloma.

24 The term "primary antibody deficiency" has been expanded to include several types of deficiency. The clinical significance of some sub-groups has only recently been recognised.
The spectrum includes:

• Common variable immune deficiency (CVID) which is the commonest serious antibody deficiency

• X-linked antibody deficiency

• IgG subclass deficiencies

• Specific antibody deficiencies

• Selective IgA deficiency.

25 The prevalence of symptomatic primary antibody deficiency is estimated at 4 per 10⁵ population.⁹ A published survey of a population genetically similar to that of Scotland suggests that 250 patients with diagnosed primary antibody deficiency should be receiving appropriate treatment.¹⁰ At present there are 8 in the Aberdeen centre, 12 in Edinburgh and 14 in the Glasgow centre. This suggests that there is a significant level of under-diagnosis which, in turn, can lead to unsuspected and under-managed infection and non-infectious complications and be a cause of chronic illness and early death. This may be due in part to the fact that only one in four hospital consultants and one in fifteen general practitioners are ever likely to see a CVID patient and some may not be fully conversant with the nature of the condition.⁹

26 In addition to the above, an increasing number of patients present with secondary immunodeficiency, due to immuno-suppression from intensive anti-cancer chemotherapy or prolonged immuno-suppression following solid organ transplantation. Immunologists are increasingly required to oversee on-going care for these types of patient.

27 There is evidence of on-going sub-optimal care for antibody deficient patients in many areas of the UK in regard to diagnosis, treatment, monitoring and follow-up.¹¹

Autoimmune Disease:

28 Autoimmune disorders are found in all population groups, can affect any organ or tissue in the body and place a substantial burden on the healthcare infrastructure of the NHS in Scotland. On an individual basis no single autoimmune disease is common, at least in comparison with other disorders such as allergy, cancer or heart disease. Collectively, however, the wide variety of defined autoimmune disorders accounts for a substantial patient workload for clinicians and a large proportion of the diagnostic activity undertaken by immunology laboratories. The spectrum includes a wide range of organ-specific and non-organ-specific disorders such as:

• rheumatoid arthritis

• systemic vasculitis

• systemic lupus erythematosus

• autoimmune thyroid disease

• insulin dependent diabetes mellitus

• autoimmune gastritis

• autoimmune liver disease

29 Rheumatic diseases alone affect 1-2% of the population and insulin dependent diabetes mellitus as many as 30 individuals per 100,000. Autoimmune thyroid disease occurs at a comparatively greater incidence, the exact figure depending on the age of the population studied.

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