Investigations
1st investigations to order
no test required: diagnosis is clinical
Test
There are no specific tests to confirm CRPS. It is principally a clinical diagnosis. Investigations may support the diagnosis or rule out differentials.[36]
Result
investigations are supportive
Investigations to consider
electromyogram
Test
May be helpful in excluding differentials by supporting the diagnosis of general or focal nerve disorders.
Result
normal in CRPS
nerve conduction studies with surface electrodes
Test
These test only the large (fast-conducting) myelinated alpha or alpha/beta fibres in mixed peripheral nerves. They do not test small A delta and C fibres, those primarily affected in CRPS. Abnormal nerve conduction studies can reveal a generalised or focal (e.g., entrapment) peripheral neuropathy affecting large myelinated fibres; this may be helpful in differential diagnosis.
Result
normal or only mildly abnormal in type 1 CRPS; significant abnormalities in type 2 CRPS
punch skin biopsy
Test
Intraepidermal unmyelinated cutaneous sensory axons can be visualised in the skin and used to assess small-fibre morphology and number. Abnormalities are common in small-fibre neuropathies and inheritable neuropathies, and are seen in CRPS patients, but they are not specific for CRPS.[39]
Result
abnormalities can be seen in cutaneous sensory axons, but the diagnostic significance is unclear
radiograph of affected limb
Test
Affected limb may show osteopenic change in underlying trabecular bone. Cortical bone is usually preserved.
Result
patchy subchondral or subperiosteal osteoporosis commonly seen in chronic cases
bone scintigraphy with technetium 99m
Test
Use is controversial because of low specificity and sensitivity.[48]
Result
diffuse asymmetric uptake or delayed image with increased asymmetrical peri-articular uptake
dual-energy x-ray absorptiometry (DXA)
Test
Full-body DXA may show regional osteoporosis.
Result
T-score of ≤-2.5 indicates osteoporosis
quantitative CT scan
Test
To assess bone texture, including quantitative assessment of bone density.
Result
normal CT scan does not exclude CRPS; occult bone injuries such as stress fractures can be diagnosed
MRI
Test
To assess soft tissues and to rule out occult bony injuries such as stress fractures or bone oedema syndromes.
Result
normal scan does not exclude CRPS; soft-tissue oedema and patchy bone changes can be consistent with CRPS
vascular studies
Test
To rule out arterial compression, or venous thrombosis or incompetence.
Investigations may include duplex ultrasonography, magnetic resonance angiography, ankle-brachial index, photoplethysmography, pulse volume recording, and ambulatory venous pressure (a global assessment of venous competence).
Result
normal in CRPS
sympathetic nerve blocks
Test
Evidence is limited.[46][47] If the upper limb is affected, the stellate ganglion is blocked with local anaesthetic. If a lower limb is affected, the lumbar sympathetic chain is blocked. A positive response in any individual patient is unpredictable.[49] Lack of response does not exclude a diagnosis of CRPS.
Result
successful block with sympathetically maintained pain; ineffective if pain is sympathetically independent
intravenous regional or selective anaesthetic blocks
Emerging tests
autonomic testing
Test
Tests including resting sweat output, resting skin temperature, and the quantitative sudomotor axon reflex test (QSART) are occasionally used, but are primarily research tools.[50]
Result
differences between affected and unaffected area
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