All patients had initial screening sensory and motor nerve conduction studies performed: median sensory, recording the second digit; ulnar sensory, recording the fifth digit; superficial radial, recording the dorsum of hand; median motor, recording the thenar eminence; and ulnar motor, recording the hypothenar eminence. As CTS was suspected in all cases, median and ulnar palmar nerve conduction studies were performed as well. All these studies were performed using previously reported techniques, and all collected values were compared with EMG laboratory control values.14,15 In all patients, the median nerve conduction studies were performed bilaterally. Approval from an ethics board or an institutional review board was not needed because this study did not involve personal information or identifiable images.
To avoid identifying small, chance asymmetries related to hypothyroidism and other conditions that produce bilateral CTS, the author predefined the degree of asymmetry required for study inclusion to identify only large asymmetries. Because the EDX manifestations of CTS typically reflect features of demyelination before those of axon loss, the required asymmetries were predefined using peak sensory and distal motor latency values. For study inclusion, the median nerve latency value recorded from the nondominant limb needed to exceed the value recorded from the dominant limb by 0.6 msec for the median palmar responses, 1.0 msec for the median digital sensory responses, or 1.0 msec for the median motor responses.
Excluded from the study were patients who reported being ambidextrous, those who had changed hand dominance at any age and for any reason, those with a history of upper extremity trauma or surgery, and those with EDX findings indicating a concomitant neuromuscular disorder. In addition, patients with diabetes mellitus or any other condition associated with bilateral CTS were excluded.
Results
From the approximately 2,000 upper extremity EDX studies performed over a 30-month period, the author identified 21 patients who met the inclusion criteria (Table 1). Of these 21 patients, 15 (71%) had bilateral CTS and 6 (29%) had unilateral CTS. Sixteen of the 21 patients used their nondominant hand, through a significant portion of the day, to perform an activity that required sustained gripping (Table 2).
Of these 16 patients, 14 reported that the sustained gripping activity was related to their occupation: pipe fitter (4 patients), card dealer (4), professional driver (2), grocery store clerk (1), wire stripper (1), bakery worker (1), and motel room cleaner (1). In their jobs, the pipe fitters were continually cutting pipe during their entire 8-hour shift—using the nondominant hand to tightly grip a pipe while using the dominant hand to direct an electrically powered blade through it. Of the card dealers, 1 was a professional playing card dealer (not the dealer whose case prompted this study), 1 distributed store coupons into containers, and 2 distributed pieces of mail into bins (referred to as casing the mail). All the card dealers used their nondominant hand to tightly grip items that the dominant limb distributed. The professional drivers used their nondominant hand to grip the steering wheel. The grocery store clerk used her nondominant hand to grip shopping items while moving them across a barcode detector. The wire stripper used her nondominant hand to tightly grip bundles of wire while holding a tool in the dominant hand to snip or strip them. The bakery worker continually used her nondominant hand to squeeze off pieces of dough from a mound. And the motel room cleaner used her nondominant hand to grip the side of a bathtub while scrubbing the tub with her dominant hand (she estimated she cleaned bathtubs for about 25% of her 8-hour shift).
Of the 2 patients who reported sustained gripping unrelated to occupation, 1 was baby-sitting her grandson 5 days per week. She carried him, grasping his buttock with her nondominant hand, while performing her daily activities. She estimated she carried the child a minimum of 2 hours a day. After several weeks, she noted episodic tingling in the nondominant hand, yet she continued carrying him for another 7 months, at which point she sought medical care. The other patient, a student in a stress relief class, was instructed to repetitively open and tightly close her nondominant hand for 10 minutes 4 or more times per day. After several weeks, she noted episodic tingling in the exercised, nondominant hand.
Of the 5 patients who denied performing an activity that required sustained gripping, 2 used their nondominant limb to enter data into a computer while turning pages with the dominant limb. A piano teacher, used her nondominant limb to strike piano keys while sitting to the right of her pupils; and a typist, consistently slept with the dorsal aspect of the nondominant hand pressed into her cheek, resulting in sustained wrist flexion throughout the night. One patient could not identify an activity performed with her nondominant limb both frequently and for prolonged periods.
