Abstract
A 40-year-old man referred to our hospital due to pain and numbness in the left thumb. Neurological findings revealed decreased tactile, temperature and pain sensations only in the left thumb. The strength of the left finger was almost normal, but the muscles associated with the thumb had a similar degree of mild weakness as pain was induced. A painful trigger point at the base of the left thumb suggested impairment of the nerve associated with thumb sensation. Nerve ultrasound was performed targeting the small nerves running from the left palm to the fingers, and local swelling was observed in the common palmar digital nerve to the left thumb. Sensory nerve conduction studies of the median nerve with thumb stimulation and wrist recording revealed decreased amplitude on the left side. Additional medical history revealed that the patient held the smartphone in his left hand and operated it with his left thumb, spending more than eight hours playing smartphone games every day. We concluded that the patient’s left thumb pain and numbness was due to common palmar digital nerve injury to the left thumb, which was caused by habitual smartphone focal nerve compression, and nerve ultrasound was helpful in its diagnosis.
