Differentials
Polymyalgia rheumatica (PMR)
SIGNS / SYMPTOMS
Typical symptoms of PMR include aching and stiffness in the shoulders and proximal limb muscles, with or without mild polyarthritis or tenosynovitis. Although GCA and PMR frequently co-exist, cranial symptoms including headache, jaw claudication, and vision symptoms are typically absent in patients with PMR. PMR typically has less prominent symptoms than GCA.
INVESTIGATIONS
No specific diagnostic tests, but diagnosis is supported by history, physical examination, and raised inflammatory markers (erythrocyte sedimentation rate >40 mm/hour). A rapid response to oral glucocorticoids makes the diagnosis more likely. The presence of symmetrical bicipital tendonopathy and/or subacromial bursopathy are suggestive of PMR as is the presence of fluorodeoxyglucose uptake on a PET scan in the limb girdles and interspinous ligament.
Solid organ cancers and haematological malignancies
SIGNS / SYMPTOMS
Clinical presentation may be similar in solid-organ cancers and haematological malignancies, especially multiple myeloma and lymphoma.
INVESTIGATIONS
A thorough physical examination, including careful breast exam should be performed as well as age-appropriate cancer screening studies (e.g., mammogram). Haematological studies including protein electrophoresis, lymphocyte immunophenotyping, and bone marrow biopsy may reveal evidence of multiple myeloma. Chest x-ray and computed tomography (CT) may reveal enlarged nodes in lymphoma.
Takayasu's arteritis
SIGNS / SYMPTOMS
The many shared histopathological features, genetic factors, and overlap in presentation of Takayasu's arteritis and GCA suggest that they may actually be variable presentations of the same disease process.[57] Traditionally, the major factors differentiating Takayasu's arteritis from GCA are age at disease onset and lack of involvement of cranial arteries. Typically occurs in young women, usually in their 20s and 30s. Although systemic symptoms are also common in Takayasu's arteritis, cranial symptoms are usually absent. Patients with Takayasu's arteritis often have absent or asymmetric peripheral pulses and multiple arterial bruits.
Occasional mild, chronic Takayasu's arteritis may not be diagnosed until after the patient is 50 years old. They may have had longstanding symptoms of decreased aortic or aortic branch outflow, such as dizzy spells, or been noted as having an unexplained lack of a pulse in one arm.
INVESTIGATIONS
MRI first line; PET, CT, and/or ultrasonography as alternatives
Chronic infection
SIGNS / SYMPTOMS
There may not be any differentiating signs or symptoms.
INVESTIGATIONS
Investigations depend on the infection being considered. These include multiple blood cultures and echocardiography for infective endocarditis, chest x-ray and sputum culture for tuberculosis, and serological tests for other chronic infections including hepatitis B and C.
Rheumatoid arthritis
SIGNS / SYMPTOMS
Symmetric small joint polyarthritis and extra-articular manifestations are characteristic of rheumatoid arthritis and distinguish this condition from GCA.
INVESTIGATIONS
May have positive rheumatoid factor and anticyclic citrullinated peptide antibodies. May have radiographic, ultrasound, or MRI evidence of joint erosions.
Amyloidosis
SIGNS / SYMPTOMS
Amyloidosis can rarely cause jaw and tongue claudication, although these are very characteristic of GCA.[58]
INVESTIGATIONS
Serum immunoelectrophoresis may show a monoclonal band. Amyloidosis is distinguishable from GCA by lack of response to therapy and by staining of a temporal artery specimen for amyloid. Rectal or abdominal fat biopsy and serum amyloid P scan may be positive.
Non-arteritic anterior ischaemic optic neuropathy (NAION)
SIGNS / SYMPTOMS
Symptoms may mimic GCA. The presence of other symptoms (e.g., PMR, headache, and jaw claudication) in the presence of elevated levels of inflammatory markers clearly distinguishes GCA from NAION.
INVESTIGATIONS
There are no specific differentiating tests.
Systemic lupus erythematosus
SIGNS / SYMPTOMS
Distinguishing features are the presence of photosensitivity, skin rash, oral ulcers, and symptoms of pleuropericarditis.
INVESTIGATIONS
May see positive antinuclear antibody, antibody to double-stranded DNA, or antibodies to extractable nuclear antigens. Laboratory evidence of cytopenias or glomerulonephritis.
Overlap connective tissue disease
SIGNS / SYMPTOMS
Distinguishing features are the presence of photosensitivity, skin rash, oral ulcers, and symptoms of pleuropericarditis.
INVESTIGATIONS
May see positive antinuclear antibody, antibody to double-stranded DNA, or antibodies to extractable nuclear antigens. Laboratory evidence of cytopenias or glomerulonephritis.
Hypothyroidism
SIGNS / SYMPTOMS
Myalgias due to hypothyroidism should respond promptly to thyroid replacement therapy; cranial symptoms are absent.
INVESTIGATIONS
Thyroid function tests may reveal low T4.
Polymyositis
SIGNS / SYMPTOMS
Proximal muscle weakness is the predominant symptom.
INVESTIGATIONS
Elevated levels of muscle enzymes and abnormalities on electromyogram.
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