CASEA 16-year-old previously healthy girl presented to the ED for evaluation of left arm soreness and paresthesias, which began 3 hours earlier. She recently completed a scuba certifi cation course and earlier that day participated in her fi rst two 30-to 45-minute cold-water quarry dives with an instructor. On her fi rst dive, she descended to 25 ft (7.6 m) and paused at 15 ft (4.6 m) on a platform before ascending. After a 45-minute break, she dove to an initial depth of 25 ft, continued to a maximum depth of more than 40 ft (12 m), then ascended to the surface without stopping at the platform. Afterward, she was extremely tired and slept for 2.5 hours. Upon awakening she noticed an aching feeling in her left arm and a tingling sensation from her bicep to her fi ngers. In the ED, she described the pain as constant and uncomfortable, like her arm was falling asleep. She did not take pain relievers and could not recall injuring her arm. She had no allergies, denied the use of any daily medications, and was a nonsmoker.On examination, the patient was well appearing. Her vital signs were: BP, 138/85 mm Hg; heart rate, 105; Spo 2 , 100% on room air; and tympanic temperature, 99.1° F (37.3° C). The physical examination was signifi cant for mild tenderness of the left mid-forearm and dorsal wrist in addition to a dull sensation when light touch was applied to the affected extremity from shoulder to fi ngers. The patient's strength was 5/5 in all extremities and her upper and lower extremity refl exes were intact (2+) bilaterally. She denied pain with movement of her left arm and her pulses were equal bilaterally. Her lungs were clear to auscultation bilaterally and her heart rate and rhythm were regular without any murmurs, rubs, or gallops.Her arm appeared normal to inspection and the remainder of the physical examination was unremarkable. A complete blood cell count, complete metabolic panel, and urinalysis were unremarkable and a urine pregnancy test was negative. An ECG showed normal sinus rhythm with a ventricular rate of 90 beats/minute.