A 48-year-old man comes to the office due to pain in his right hand. He has had symptoms intermittently for the last year, but they have become worse over the last 3 months, particularly at night. The pain radiates to the anterior aspect of the forearm. Medical history is notable for type 2 diabetes mellitus; his most recent hemoglobin A1c was 8.5%. The patient does not use tobacco, alcohol, or illicit drugs. He works at a retail supermarket where he is responsible for stocking heavy canned goods. Blood pressure is 148/95 mm Hg, pulse is 76/min, and respirations are 12/min. BMI is 32 kg/m². On examination, the patient is mildly obese but otherwise appears comfortable. There is weakness of thumb opposition and slightly decreased light touch sensation over the palmar surface of the tip of thumb, index finger, and long finger. Sensation is normal in the remaining fingers and forearm. Which of the following is the most likely cause of this patient's symptoms?

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11ec25c8_d573_de10_bc81_e3b27e56f242_MD0003_00 This patient has pain and decreased sensation in the hand, consistent with carpal tunnel syndrome (CTS). CTS is caused by compression of the median nerve as it passes deep to the flexor retinaculum in the wrist, typically due to swelling of the flexor tendons, fibrosis or edema of the surrounding soft tissues, or extrinsic deformity (eg, arthritis in the wrist joint). CTS is common in patients with diabetes mellitus, as well as in individuals with repetitive, forceful use of the wrist and hand. flexor retinaculum Manifestations of CTS include paresthesia, pain, and sensory loss in the palmar aspect of the first 3 digits and sometimes the lateral aspect of the fourth; patients may also have referred pain to the lateral palm, forearm, or even upper arm. However, because the palmar cutaneous branch of the median nerve passes outside the carpal tunnel, the sensation over the thenar eminence typically remains intact. palmar cutaneous branch sensation over the thenar eminence In the clinic, symptoms may be provoked by percussion over the nerve or forceful flexion of the wrist (Tinel and Phalen tests, respectively). Early CTS typically has an intermittent course with symptoms often worse at night. However, manifestations can be highly variable, particularly with severe disease. As the disorder progresses, symptoms may become persistent and/or associated with motor features (eg, thenar atrophy, weakness of thumb abduction and opposition). Tinel and Phalen tests thenar atrophy (Choice A) Complex regional pain syndrome causes pain in a regional (not dermatomal) distribution. It typically follows trauma or surgery and is associated with edema, vasomotor signs, and trophic changes in skin and hair. (Choice B) Multiple sclerosis is caused by focal demyelination in the white matter. The clinical features (eg, sensory disturbances, incontinence, optic neuritis) are intermittent and progressive, and occur in multiple neural distributions. (Choice C) Glycosylation of proteins in vasa nervorum leads to diabetic peripheral neuropathy. It causes pain in the extremities but usually occurs in a stocking-and-glove pattern; findings tend to be most prominent in the feet. (Choice E) Proximal median nerve compression in the forearm (eg, pronator teres syndrome) results in forearm pain and sensory loss over the entire lateral palm and thenar eminence. Educational objective: Carpal tunnel syndrome is caused by compression of the median nerve at the wrist. It initially has an intermittent course, but with progression the symptoms may become more persistent and associated with motor features. Pain may radiate to the forearm or upper arm, but sensory loss in these areas is not seen. References: Pathophysiology of carpal tunnel syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/25630774) Occupational and biopsychosocial risk factors for carpal tunnel syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/25046324)

A 48-Year-Old Man Comes to the Office Due to Pain