Giant Cell Arteritis

Giant Cell Arteritis

(Temporal Arteritis)

Definition

Giant cell arteritis (GCA) also known as temporal arteritis is an autoimmune disease. Autoimmune diseases are conditions in which immune cells, that normally help fight infections, are misdirected to attack  own tissues. In the case of GCA, these immune cells are involved in an inflammatory reaction in large arteries of the body, mainly branches of the aorta and often, the aorta itself. The inflammation damages the affected blood vessels.  At present the exact cause of this condition is unknown.

GCA is a form of vasculitis. Vasculitis is defined as a condition in which blood vessels, particularly arteries, become inflamed.  In GCA, the aorta and its branches are usually affected. The inflammation in GCA can cause swelling of the blood vessel wall and narrowing of the blood vessel lumen causing decreased blood supply to the neighboring tissues.  The blood vessel may also become thrombosed causing severe ischemia or necrosis of tissues ordinarily supplied by the blood vessel.

Etiology

The etiology of temporal arteritis is multifactorial and is determined by both environmental and genetic factors. Data indicate that the disease is probably initiated by exposure to an exogenous antigen. Numerous viruses and bacteria have been proposed as potential precipitants, including parvovirus, parainfluenza virus, varicella zoster virus, Chlamydia pneumoniae, and Mycoplasma pneumoniae.

T cells are recruited to the vessel wall after initial exposure to the antigen. They release cytokines that act on local macrophages and multinucleated giant cells.^[4]The response of the macrophages and multinucleated giant cells to the cytokines depends upon their location within the vessel wall.

Adventitia-based macrophages produce interleukin-6 (IL-6), which further augments the inflammatory cascade. Macrophages within the media produce oxygen free radicals and metalloproteases, which degrade the arterial wall and fragment the elastic lamina. With the disruption of the internal elastic lamina, the intima becomes accessible to migrating myofibroblasts, which proliferate and lay down extracellular matrix.

This migratory process is driven by intima-based macrophages that produce platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF). The net effect of these events is an arteritis with local vascular destruction and intimal hyperplasia leading to luminal stenosis and occlusion. The exuberant release of cytokines associated with this process may be responsible for the constitutional symptoms frequently encountered with the disease

Pathogenesis

Histologically, the inflammatory reaction is granulomatous with highly activatedmacrophages and T lymphocytes, of which CD4+ T cells are in the majority. Despite its name, giant cells are not a prerequisite for the diagnosis. The local activation of CD4+ T cells in the outer layers (adventitia) of the vessel wall is suggestive of an antigen-driven disease. The possible antigen might be of external origin, but it may also be autologous. Theadventitia was proposed to be the centre of the immune response, with the vasa vasorum being the port of entrance of the antigen-presenting cells. The adventitial macrophages and T lymphocytes produce high levels of cytokines, thereby promoting further inflammatory reaction, but not tissue destruction.

 The macrophages of the media, on the other hand, produce metalloproteinases and oxygen radicals, leading to the disintegration of elastic laminae and further injury of the vessel wall. The tissue cytokine patterns of the temporal artery were correlated with clinical phenotypes of the disease. Thus, high levels of the cytokine interferon-c (IFN-c) correlated with cranial symptoms, whereas patients with systemic symptoms only, displayed low levels of this cytokine. Growth factors, such as platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF) are both amply expressed in the inflammatory infiltrate, stimulating intimal hyperplasia. Interestingly, these factors were also produced by the multinucleated giant cells, which are, therefore, not only removers of debris but also secretory.

Thus, the vascular pathology in GCA is the result of immunological injury to the vessel wall, as well as stromal response within the arterial wall. Moreover, significant media atrophy and calcification of the internal elastic membrane (IEM) appear to be prerequisites for its occurrence. The hallmarks of GCA are the systemic inflammation and the inflammatory infiltrate of the vessel wall, resulting in luminal narrowing and end-organ ischaemia.

The most feared acute complications include blindness and infarcts of various vascular territories, whereas the development of mural weakness, resulting in aortic dissection, has been considered a late manifestation.

Modern history of giant cell arteritis runs along two paths; that of temporal arteritis (TA) and that of polymyalgia rheumatica (PMR). There is still a controversy over whether PMR and GCA (TA) are linked entities, and specifically if PMR is a vasculitis. Several contributions over the last decade have indicated a similar pathogenetic process in the two conditions. Analyses of the temporal artery biopsies have shown similar patterns of T-cell and macrophage-derived cytokines winterleukin (IL)-1b, IL-6, transforming growth factor-b (TGF-b), IL-2x in biopsy-negative PMR patients as well as in patients with biopsy-proven GCA, but not in agematched controls. However, IFN-c was not found in PMR patients, but only in the TA patients, indicating that IFN-c might be crucial for the development of an overt granulomatous process w9x. These data indicate that PMR patients have a subclinical vasculitis and therefore PMR has been regarded as a ‘formefruste’ with minor vascular involvement.

According to a recent study, using positron emission tomography (PET) with fluoro-18-deoxyglycose (18F-glycose), there was a significantly increased vascular uptake in the large thoracic arteries (aorta, subclavian and carotid arteries) also in PMR patients without clinical or morphological evidence of inflammation in temporal arteries. This investigation gave further support to the contention that PMR and TA are two different expressions of the same underlying disorder and that the large arteries, and notmerely the temporal arteries, may be affected in both conditions.

Epidemiology

Incidence

·         0.22 new cases/year/1000 population aged >50 years

·         The incidence fluctuates in a cyclical pattern

Prevalence

·         2/1000 population.

·         Demographics

Age

·         Almost exclusively affects those >50 years

·         Incidence increases with age

GCA is markedly age-restricted. Essentially, no cases younger than 50 yr of age have been identified and the likelihood of being diagnosed with this disease increases continuously with age. GCA is about 20 times more common among people in their 9th decade compared with people aged between 50 and 60 yr, which may indicate that its pathogenesis is related to the ageing of the arterial wall. Immunosenescence, the term used for changes in the immune system with ageing, implies a decline in immunocompetence, resulting in an increased risk of infections and autoimmuno inflammatory disorders. Furthermore, a decreased antibody (Ab) production and a shortened duration of protective immunity following immunization are characteristic features in the elderly. Despite much research in this field, basic mechanisms of age-related immune dysfunction have notbeen clarified. Recently, it was demonstrated that elderly people who failed to produce specific Abs following influenza vaccination showed a predominance of CD8+ CD282 T cells. The aetiology of the CD282 T-cell recruitment is not fully understood in healthy individuals, but

there is evidence that these cells might be a response to continued antigenic stimulation. An increased number of autoreactive CD8+ CD282 T cells leads to the production of large amounts of IFN-c, which might trigger an imbalance in the production of T helper 1 (TH1) and TH2 cytokines, and a polarization towards the TH1 effector type with higher age.

Furthermore, in the elderly there is a reduced production of adrenal and gonadal steroids, resulting in less inhibitory effects on pro-inflammatory cytokine production. Changes have

also been reported in the activity and reactivity of the hypothalamus–pituitary–adrenal axis. It has been speculated that an imbalance in the production of pro- and anti-inflammatory cytokines could reduce the protection against infections in elderly people and also increase the risk of developing other age-related disorders such as Alzheimer’s disease and atherosclerosis.Exactly how the ageing of the immune system affects immune reactivity in a patient with GCA has not been investigated.

Gender

·         Women are two or three times more likely to be affected as men.

There is a clear female predominance in GCA, with 2- to 3-fold more women than men. Thisdifference appears to be more marked in the northernparts of Europe. Only in one Spanish study were malesreported to be predominant in GCA . Evidence was recently presented indicating that other types of primaryvasculitides display an inverse gender preference. Anepidemiological review of Wegener’s granulomatosis,Churg–Strauss syndrome and polyarteritisnodosa in theUnited Kingdom, Spain and Norway showed that, in allareas and in all disease categories, the incidence was higher in men than women, with a peak incidence at theage of 65–74 yr. These vasculitides affect mediumsized and small vessels, in contrast to GCA, whichaffects large and medium-sized arteries. Consequently,although all these disorders display a peak incidence inelderly people, there appear to be different genderrelatedfactors behind the initial immune stimulation in the two disease groups.

·         Impact of the female sex hormones

Since GCA is a disorder among elderly females, the question might be raised of whether sex hormones are involved in its pathogenesis. Interestingly, a recent epidemiological studyrevealed that the number of pregnancies was lower among GCA patients than among controls. It was suggested that the hyperoestrogenic state during pregnancy protects the

artery wall. Oestrogen is involved in a wide variety of different mechanisms which, theoretically, may be related to GCA. It is thus known to preserve a normal vessel wall by stimulating as well as inhibiting the growth of vascular smooth-muscle cells and there is evidence that it influences the immune system. One recent study showed that mononuclear and giant cells in GCA display the cytoplasmic accumulation of oestrogenreceptor-a (ER-a). Cytoplasmic ER-a was also seen in media smooth muscle in GCA and in non-GCA controls. The nucleotide sequence analysis of the ER-a gene revealed no differences between GCA patients and controls. Whether the reduction in circulating oestrogen in post-menopausal women plays a role in the development of the asymmetrical loss of smooth-muscle cells in

the temporal arteries and IEM calcification, which appear to be a prerequisite for the disorder.

Race

·         Almost exclusively affects Caucasians of northern European origin.

·         Rare in African-Americans.

·         The highest figures worldwide were documented from Southern Norway

Genetics

·         There may be a genetic tendency to giant cell arteritis - familial clusters have been found.

The possibility of a genetic influence on GCA susceptibility was initially supported by reports of cases among first-degree relatives. Several studies have shown an association of GCA incidence, and risk of visual complications, with the HLA-DRB1*-04 alleles.

However, in isolated PMR, without GCA symptoms, the HLA class II expression varied from one population to another w26x. Genetic polymorphisms with regard to the expression of tumor necrosis factor (TNF), intercellular adhesion molecule (ICAM-1), regulated on activation, normal T-cell expressed and secreted (RANTES) and interleukin receptor antagonist IL-1Ra were also shown to influence the susceptibility for GCA and PMR, irrespective of DRB1 type

Geography

·         There is a tendency toward increased rates of disease  in northern countries

The incidence of GCA varies greatly in different geographical areas. It has repeatedly been shown that the disease predominately affects subjects of Northern European descent, in particular those of Nordic heritage, irrespective of their place of residence, with estimates of about 20 cases annually per 100 000 persons older than 50 yr of age. The incidence rates are lower in Southern Europe. Only a few cases are reported in Israel and in black populations, while in Asian countries GCA is distinctly infrequent.

Clinical findings and Diagnosis

Most patients with GCA will have one or more of the symptoms listed below. However, in a minority of patients these symptoms are absent or develop late in the course of the disease making the diagnosis of underlying GCA a challenge.

Common symptoms

·         New headache, usually in the temples

·         Tenderness of the scalp

·         Swelling of the arteries near the temples

·         Vision changes like a curtain in the field of vision, sudden vision loss (temporary or permanent) or double vision.

·         Pain in the muscles of the jaw while chewing food

·         Shoulder or hip joint aching and stiffness

·         Weight loss

·         Poor appetite

·         Low grade temperatures

Less common symptoms

·         Cramping or aching in the arms with activity

·         Audible pulsations (bruits) over the axillary areas

·         Cramping or aching in the legs while walking which improves with resting

·         Dry cough or sore throat

·         Stroke-type symptoms

Physical examination. 

In addition to symptoms physical examination should be performed, paying particular attention to patient’s temporal arteries. Often, one or both of these arteries are tender with a reduced pulse and a hard, cord-like feel and appearance.

Differential Diagnosis

The differential diagnosis for a patient who presents with only the systemic inflammatory symptoms of temporal arteritis is broad. Systemic infections, connective tissue diseases, and malignancies may have similar clinical features. Primary systemic amyloidosis can mimic the symptoms of both PMR and temporal arteritis. Patients with a monoclonal band on immunoelectrophoresis and a poor response to systemic corticosteroids should have a Congo red stain performed on a temporal artery biopsy.

The ophthalmic features of temporal arteritis can be mimicked by nonarteritic anterior ischemic optic neuropathy (NAION), a disease characterized by visual disturbances in patients with cardiovascular risk factors and a susceptible ”crowded” optic disc.

Several features can be used to differentiate NAION from temporal arteritis. NAION typically occurs in a younger age group (mean age, 60 years). Constitutional symptoms are absent in NAION, and the ESR and CRP level are within normal limits. The visual changes in NAION are less severe and typically do not result in complete vision loss. On ophthalmic examination, the cup-disc ratio is reduced in NAION (hence the description of the optic disc as ”crowded”), whereas it is normal in temporal arteritis.

Several vasculitides and connective tissue disorders can present with similar systemic and ophthalmic manifestations, including systemic lupus erythematosus (SLE), rheumatoid arthritis, polyarteritisnodosa, Churg-Strauss syndrome, microscopic polyangiitis, Takayasu arteritis, and polymyositis. Differences in systemic organ involvement, microscopic findings, and distribution of lesions can help distinguish these entities from temporal arteritis.

Compressive intracranial lesions, both malignant and benign, may also be considered in the differential; these can be ruled out with neuroimaging studies.

Laboratory Tests

·         Blood tests. 

If your doctor suspects giant cell arteritis, you're likely to have a blood test that checks your erythrocyte sedimentation rate — commonly referred to as the sed rate. This test measures how quickly red blood cells fall to the bottom of a tube of blood. Red cells that drop rapidly may indicate inflammation in your body.

You may also have a test that measures C-reactive protein (CRP), a substance your liver produces when inflammation is present. The same tests may be used to follow your progress during treatment.

·         Biopsy.

The best way to confirm a diagnosis of giant cell arteritis is by taking a small sample (biopsy) of the temporal artery. Because the inflammation may not occur in all parts of the artery, more than one sample may be needed. The procedure is performed on an outpatient basis during local anesthesia, usually with little discomfort or scarring. The sample is examined under a microscope in a laboratory.

If you have giant cell arteritis, the artery will often show inflammation that includes abnormally large cells, called giant cells, which give the disease its name. Unfortunately, a biopsy isn't foolproof. It's possible to have giant cell arteritis and still have a negative biopsy result. If the results aren't clear, your doctor may advise another temporal artery biopsy on the other side of your head.

Although a temporal artery biopsy is the standard test for diagnosing giant cell arteritis, imaging tests may also be used for diagnosing giant cell arteritis and for monitoring treatment. Possible tests include:

The above image is a biopsy of the temporal artery shows inflammation almost completely closing the opening of the artery.

·         Magnetic resonance angiography (MRA). 

This test combines the use of magnetic resonance imaging (MRI) with the use of a contrast material that produces detailed images of your blood vessels. Let your doctor know ahead of time if you're uncomfortable being confined in a small space because the test is conducted in a tube-shaped machine.

·         Doppler ultrasound. 

This test uses sound waves to produce images of blood flowing through your blood vessels.

·         Positron emission tomography (PET). 

Using an intravenous tracer solution that contains a tiny amount of radioactive material, a PET scan can produce detailed images of  blood vessels and highlight areas of inflammation.

 Treatments

GCA is a highly corticosteroid-responsive disorder. A majority of the patients experience an excellent therapeutic effect. Moreover, this treatment has a preventive effect on vascular complications, as has clearly been shown in many long-term follow-up studies.

The time before the initiation of corticosteroid treatment was the single most important factor predicting outcome in patients presenting with symptoms of visual impairment. Among those who were treated within 24 h after loss of sight, an improvement was achieved in more than 50%. In contrast, only 6% of the patients improved when treatment was delayed for more than 24 h. Schmidtemphasized the importance of an early diagnosis and prompt corticosteroid treatment. They reported six cases with severe vascular complications (bilateral blindness, cerebral strokes) on which corticosteroid treatment had no effect. The patient delay between first symptoms (PMR, jaw claudication, headache, amaurosisfugax) and the vascular complication was on average 7 weeks. When a vascular catastrophy is manifest, the corticosteroid therapy,whatever dose chosen, may prevent another vascular incident but does not reverse the symptoms of the first accident. The optimal initial dose regimen of oral prednisolone, which is the drug most frequently used, has been discussed. According to prospective large series applying acceptable diagnostic criteria, and using predefined treatment protocols, 20–60 mg of prednisolone (mostly 40–60 mg) was shown to be an appropriate starting dosage in about 90% of cases. Alternate-day administration regimens of corticosteroids have not proved effective in GCAand this treatment does not reduce the development of steroid-induced osteoporosis.Treatmentwith intramuscular methylprednisolone was reported to result in a more beneficial side-effect

Major Side effects of corticosteroid therapy

·         Osteoporosis

·         High blood pressure

·         Muscle weakness

·         Glaucoma

·         Cataracts

Other possible minor side effects of corticosteroid therapy include:

·         Weight gain

·         Increased blood sugar levels, sometimes leading to diabetes

·         Thinning skin and increased bruising

·         Weakened immune system, leading to susceptibility to infection and delayed healing

New drugs such as TNF blockers have rapidly emerged as efficient treatments in GCA. Regarding their use in GCA, the experience is limited to case reports, albeit with some encouraging results. Cantini et al. reported a complete response in three of four patients with long-standing active giant cell arteritis, still requiring high doses of prednisolone after more than 42 months. All patients had developed serious corticosteroid-related side-effects. After two infusions with infliximab (3 mgukg), three of the patients displayed a clinical and humoral remission. The remission sustained after a third infusion and during a follow-up time of 6 months, despite withdrawal of the corticosteroids. One patient, who did not respond to therapy, was withdrawn after the second infusion, in accordance with the protocol. The therapy was well tolerated by all patients. No side-effects were reported. Interestingly, the same group recently reported a similar good response with normalization of clinical and serological activity after three infusions with infliximab in three of four patients with persistent PMR, without cranial symptoms w98x, whereas one patient had a partial effect. In the good responders corticosteroid therapy was terminated and in the partial responder it was reduced by 50%. The remission was sustained at the control 1 yrafter the first infusion. Infliximab was well tolerated; there were no side-effects. These open pilot studies suggest that TNF-a blockade may have a steroid-sparing effect in patients with corticosteroid-resistant GCA. In a critical review of treatment studies, it was suggested that only about 10–15% of patients have a ‘corticosteroid-resistant’ disease, defined as a daily

requirement of >15–20 mg of prednisolone more than 2 months after the start of therapy . These patients require a safe and effective additional agent. Future trials should focus on appropriately defined large cohorts of patients, ideally biopsy-proven patients, who need >15 mg of prednisolone as chronic maintenance treatment. The rate of remission in the long run is another important issue which must be focused on increasingly in new treatment modalities. The characteristic prompt relief of symptoms and preventive effect on vascular complications after the initiation of corticosteroid therapy in the vast majority of patients indicates the unique role of steroid-mediated immunosuppression in GCA. Corticosteroids have been regarded as the cornerstone in the therapy of GCA and today there is little evidence, if any, that they can or should be replaced. On the other hand, despite good

clinical improvement in the systemic signs of the disease, the inflammatory infiltrate persists for a long time in the vessel wall, which further emphasizes the need for optimized therapy in GCA.

Recently, the biological action of corticosteroids was elucidated, using temporal arteries with biopsy-proven GCA explanted into immunodeficient SCID mice. NFkB-dependent cytokines (IL-2, IL-1b, IL-6) were suppressed, whereas TGF-b and IFN-c did not appear to be influenced, despite high doses of corticosteroid treatment. These observations provide an explanation for thepromptness of the therapeutic effect seen in glucocorticosteroidtreatment, but they also indicate why patients have to be treated for a long time. Persistent disease is evidenced by active histological lesions, as well as by the fact that patients develop aortic aneurysms even years after they were considered to be in remission.

Complications and Outcomes

Complications

Giant cell arteritis can cause the following complications:

·         Blindness.

 This is the most serious complication of giant cell arteritis. The swelling that occurs with giant cell arteritis narrows your blood vessels, reducing the amount of blood — and, therefore, oxygen and vital nutrients — that reaches your body's tissues. Diminished blood flow to your eyes can cause sudden, painless vision loss in one or, in rare cases, both eyes. Unfortunately, blindness is usually permanent.

·         Aortic aneurysm. 

Having giant cell arteritis increases your risk of aneurysm. An aneurysm is a bulge that forms in a weakened blood vessel, usually in the aorta, the large artery that runs down the center of your chest and abdomen. An aortic aneurysm is a serious condition because it may burst, causing life-threatening internal bleeding. Because it may occur even years after the initial diagnosis of giant cell arteritis, your doctor may monitor the health of your aorta with annual chest X-rays or other imaging tests, such as ultrasound, CT scan or MRI.

·         Stroke.

 In some cases, a blood clot may form in an affected artery, obstructing blood flow completely, depriving part of your brain of necessary oxygen and nutrients, and causing stroke. This serious condition is an uncommon complication of giant cell arteritis.

Outcomes

       Giant cell arteritis is usually a self-limiting disease with a variable duration of months to years. However, in a subset of patients the disease may follow a protracted course, requiring long-term treatment with glucocorticoids. To date, glucocorticoids are the only agents whose efficacy has been unquestionably proven. More specifically, they can both improve the clinical symptoms of giant cell arteritis and also prevent its complications, including visual loss. Glucocorticoids therapy is notoriously fraught with numerous side effects, therefore it is sensible to taper glucocorticoids as quickly as possible. Flares are not uncommon and tend often to occur upon tapering of glucocorticoids dosage or on withdrawal of glucocorticoids therapy.

     However, in most cases flares are mild and appear to respond favorably to an increase in glucocorticoids dosage or reintroduction of glucocorticoids therapy, respectively. Mortality rates of giant cell arteritis patients are comparable to those of the general population, but there is evidence for an increased frequency of potentially life-threatening ischemic events, such as myocardial infarction and cerebro-vascular accidents, especially early on in the disease course. The risk conferred by the disease appears to decrease with time, presumably as a consequence of glucocorticoids treatment, whereas it can remain significantly elevated in patients whose disease activity is not sufficiently controlled by the treatment. By contrast, there is no evidence that giant cell arteritis is associated with an increased prevalence of malignancies or that it may represent a paraneoplastic syndrome.

 References

·         Robbins and Cotran Pathologic Basis of Disease -8^th edition

·         Davidson’s Principals & Practices in Medicine – 21^st edition

·         American journal of Rheumatology - 2010 release

·         SLMC- Vascular diseases – 2008 release

·         http://www.ncbi.nlm.nih.gov

·         http://www.mayoclinic.com/health/giant-cell-arteritis/DS00440/DSECTION=lifestyle-and-home-remedies

·         http://www.vasculitisfoundation.org

·         http://emedicine.medscape.com

·         http://www.mayoclinic.com/health/giant-cell-arteritis/ 

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