A 45-year-old man comes to the office due to intermittent pain and numbness in the right hand for the last several months. The symptoms occur primarily at night and occasionally wake the patient. Shaking the hand or holding it in a dependent position briefly relieves the pain. He works as a carpenter. The patient has a 20-pack-year smoking history but does not use alcohol or illicit drugs. Vital signs are normal. BMI is 36 kg/m². Examination shows normal range of motion in the wrists and digits. Sensation is decreased to pinprick in the thumb and index finger. Biceps, triceps, and brachioradialis reflexes are normal. There is no muscle atrophy. Phalen and Tinel tests do not provoke symptoms. The remainder of the examination is normal. Which of the following is the most appropriate next step to confirm the diagnosis in this patient?

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11ec25c8_d2b6_b957_bc81_8d2decb838ae_MD0003_00 The carpal tunnel is bounded by the carpal bones and transverse carpal ligament. It contains the median nerve, along with the tendons of the flexor digitorum profundus and superficialis and the flexor pollicis longus. Compression of the nerve causes carpal tunnel syndrome (CTS), which is characterized by pain and paresthesia in the first 3 digits and the radial half of the fourth. The symptoms are often intermittent and worse at night and may be provoked by repetitive or forceful hand and wrist use, as in this patient, who is a carpenter. Patients may report relief from shaking the hand. The diagnosis of CTS is usually made on clinical grounds. Provocative measures, including tapping over the median nerve at the wrist (Tinel test) or holding the wrists in extreme flexion with the dorsum of the hands pressed together (Phalen test), often reproduce the symptoms. However, the sensitivity and specificity of these maneuvers are limited. If examination findings are inconclusive, the diagnosis can be confirmed with nerve conduction studies, which have high sensitivity and specificity for CTS; typical findings include slowed conduction velocities in the median nerve across the wrist. Imaging is not routinely indicated, although ultrasound may show swelling of the median nerve. (Choice A) CT scan of the chest can confirm malignancy at the superior pulmonary sulcus (ie, Pancoast tumor), which can cause hand pain and paresthesia due to compression of the C8-T2 nerve roots. However, the pain is typically constant and progressive, does not follow the distribution of the median nerve, and is often associated with shoulder pain, Horner syndrome (ipsilateral ptosis, miosis, anhidrosis), and supraclavicular lymphadenopathy. (Choice B) MRI of the cervical spine is indicated to evaluate cervical radiculopathy (neck and upper arm pain, diminished reflexes) or cervical spondylotic myelopathy (bilateral upper motor neuron weakness, bilateral sensory deficits). (Choices C and E) MRI allows visualization of the contents of the carpal tunnel but is indicated primarily when a mass is suspected. X-ray may be considered in patients with a history of significant trauma or evidence of advanced rheumatoid or osteoarthritis (eg, decreased range of motion, wrist joint deformity) but cannot confirm or exclude the diagnosis of CTS. Educational objective: Compression of the median nerve at the wrist causes carpal tunnel syndrome, which is characterized by pain and paresthesia in the first 3 digits and the radial half of the fourth. The diagnosis is usually made on clinical grounds, but nerve conduction studies can confirm the diagnosis. References: Carpal tunnel syndrome: diagnosis and management. (http://www.ncbi.nlm.nih.gov/pubmed/28075090)

A 45-Year-Old Man Comes to the Office Due to Intermittent