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The density of the sensory receptors (called innervation density) is assessed by two-point discrimination where two points on the skin, typically a few millimeters apart, are stimulated simultaneously. The threshold is the distance at which the patient perceives 2 separate stimuli. In thoracic outlet syndrome, vibration and pressure thresholds will typically be abnormal during provocation maneuvers but normal at rest.

X-ray of cervical spine - to identify any bony abnormalities that may be the cause of pain, including:

• degenerative cervical spine disease
• spinal disk abnormalities (e.g., narrowing of the disk space)
• abnormal C7 transverse processes
• arthritic changes

CT/MRI of the brachial plexus - there is a lack of consensus regarding the efficacy of traditional CT/MRI. Hi-speed multidetector CT is being studied since its resolution is very clear and new computer techniques offer novel ways of imaging layers of tissue. CT may reveal other conditions that may cause symptoms of TOS.

Electrophysiologic tests - tests used to measure muscle response to stimulation of nerves. These tests remain controversial and have not generally gained acceptance since they're subject to inaccuracy. Sometimes they are employed for diagnosis of late stages of TOS. Some clinicians also feel that since electrodiagnostic testing is helpful in the diagnosis of carpal and cubital tunnel syndrome, both of which are frequently found with TOS, there is some value of these tests for confirming TOS in an indirect manner.

Anterior scalene block - the anterior scalene muscle is injected with a nerve block and if the symptoms abate, it may indicate that the pain is due to muscle spasm, not TOS.