Differentials
Hypothyroidism
SIGNS / SYMPTOMS
May show signs of muscle and joint pain, weakness in the extremities, and fatigue; however, delayed relaxation of deep tendon reflexes is strongly suggestive of hypothyroidism.
May mimic chronic pain syndromes, particularly fibromyalgia, which is often associated with change in weight and depression.
INVESTIGATIONS
An elevated thyroid-stimulating hormone and low T4 suggests hypothyroidism.
Polymyalgia rheumatica (PMR)
SIGNS / SYMPTOMS
Presents with history of neck, shoulder girdle, and/or hip girdle stiffness and pain, occurring in patients more than 50 years of age, commonly female. Patients complain of difficulty rising from seated or prone positions, varying degrees of muscle tenderness, shoulder/hip bursitis, and/or oligoarthritis.
Rapid improvement is almost invariable within 24 to 48 hours with low-dose prednisolone. Approximately 10% of patients with PMR have giant cell arteritis (GCA); 40% to 60% of GCA patients have PMR.[47][48]
INVESTIGATIONS
Diagnosis of PMR is made via history and with supportive laboratory tests indicating an elevated erythrocyte sedimentation rate or C-reactive protein.
Giant cell arteritis (GCA)
SIGNS / SYMPTOMS
New-onset unilateral headache, jaw claudication associated with chewing tough foods, diffuse mandibular discomfort, dental discomfort, sinus pain and pressure, and/or tongue pain are associated with GCA. Blindness, diplopia or blurry vision, and an abnormally thickened, tender, erythematous, or nodular temporal artery are also found. Patients more than 50 years old with new-onset headache should be screened for GCA or temporal arteritis. Approximately 10% of patients with PMR have GCA; 40% to 60% of GCA patients have PMR.[47][48]
INVESTIGATIONS
Elevated erythrocyte sedimentation rate or C-reactive protein. A positive temporal artery biopsy showing a granulomatous vasculitis confirms the diagnosis of GCA. Diagnostic and therapeutic corticosteroid trial.
Polymyositis
SIGNS / SYMPTOMS
Symmetrical weakness of shoulder and pelvic girdles.
INVESTIGATIONS
Elevated muscle enzyme levels (e.g., CK) often with a positive antinuclear antibody (ANA) titre.
Characteristic changes in electromyogram (EMG) associated with polymyositis include increased needle insertional activity, spontaneous fibrillations, low-amplitude short-duration polyphasic motor potentials, and complex repetitive discharges.
Diagnosis is confirmed with muscle biopsy, indicating immune cell infiltration and destruction of muscle fibres.
Depression
SIGNS / SYMPTOMS
Depression is diagnosed clinically with a finding of more than 5 of the following symptoms, present during the same 2-week period: depressed mood, anhedonia, weight changes, libido changes, sleep disturbance, psychomotor problems, low energy, excessive guilt, poor concentration, and suicidal ideation. Depression may be associated with degrees of anxiety disorder, which may be associated with muscular tension.
INVESTIGATIONS
No differentiating tests.
Paraneoplastic syndrome
SIGNS / SYMPTOMS
Primary or secondary tumours in bone, joints, involving nerves, tendons, the head and neck, major organs, or soft tissues present with constitutional symptoms and proximal muscle pain. Paraneoplastic syndrome symptoms usually do not respond to analgesia or corticosteroid treatment. A thorough tumour work-up should be performed in patients who are unresponsive to first-line chronic pain treatment, as removal of the tumour may lead to a resolution of symptoms. Cancer may also result in neural impingement, causing radiculopathy or myelopathy.
INVESTIGATIONS
Tumour screening includes routine baseline tests including chest x-ray, full blood count, chemistry panel, and urinalysis. Age-appropriate cancer screening tests should also be performed (i.e., fecal occult blood testing, colonoscopy, mammogram). Additional specialised testing should be directed by the history, examination findings, and abnormalities found on the routine chest x-ray and laboratory tests. Sagittal MRI effectively identifies multi-level metastatic spinal disease. Other specific tests as directed by clinical evaluation.
Lambert-Eaton syndrome
SIGNS / SYMPTOMS
Proximal muscle weakness and fatigue. May show autonomic dysfunction (dry mouth, orthostatic hypotension, ptosis).
INVESTIGATIONS
Positive serology for associated autoantibodies (e.g., anti-VGCC, anti-SOX-1, anti-AChR)
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