Acta neurol. belg., 2001, 101, 232-233 Ulnar nerve lesions are commonly encountered by the electromyographer and occasionally repre- sent a dilemma since routine studies of the ulnar nerve often provide inadequate information to localize an ulnar nerve lesion in the forearm or wrist. The distal ulnar nerve gives off the dorsal sensory branch in the distal forearm, the dorsal ulnar cutaneous nerve (DUCN). Focal injury to the DUCN may more frequently occur than has been previously thought because DUCN is positioned such that it can receive acute trauma or be chroni- cally traumatized while writing, wearing a tight wristwatch band, or after hand-cuff injury. We pre- sent a thirty-nine year-old man complaining of sen- sation loss on the dorsal aspect of his last two fin- gers. His complaints started two months ago when a heavy object fell on his forearm. A thirty-nine year-old right handed man has been admitted to our EMG laboratory because of sensation loss on the dorsal aspect of the fourth and fifth digits of his left hand. His complaints started two months ago when a heavy object fell on his forearm. He had no weakness and there was senso- ry loss on the dorsal aspect of his last two fingers. Nerve conduction studies revealed an absent left DUCN response. The right DUCN response was easily obtainable by the method described by Jabre (Jabre et al., 1980). Motor evoked potentials of the left ulnar nerve with stimulation at the wrist and recording from abductor digiti quinti(ADQ) and first dorsal interosseus (DI) muscles showed a nor- mal amplitude and distal latency. Ulnar motor and sensory conduction velocities measured in the tract across the elbow (from 5cm proximal to 5 cm distal to the sulcus ulnaris) and the tract below the area from elbow to wrist were within normal limits (Table 1). Left median sensory and motor conduction studies demonstrated no abnormality. Needle EMG of the left ADQ and flexor carpi ulnaris (FCU) muscles showed no activity at rest. Recruitment and morphology of motor units were also within normal limits. The DUCN branch of the ulnar nerve is the sen- sory branch of the dorsal medial hand (Hoffman et al., 1988). This sensory branch leaves the main trunk at an average of 6 to 8 cm proximal to the ulnar styloid and becomes cutaneous as it passes between the FCU tendon and ulna but DUCN may also anomalously arise from superficial radial nerve (Peterson et al., 1992). The DUCN supplies sensation to the dorsal ulnar aspect of the wrist and hand and to the dorsal sur- face of the last two digits. Preservation of sensation on the dorsal ulnar aspect of the hand is a recog- nized clinical finding in nerve lesions to the distal forearm or wrist, ie, below the origin of the dorsal ulnar cutaneous branch of the nerve (Kim et al., 1981). In DUCN conduction studies, it is important to use a standardized technique and to measure and maintain optimal temperature of the arms under study to prevent erroneous results and misdiagnosis (Young et al., 2000). DUCN conduction is useful in identifying distal ulnar lesions, especially those within or just proximal to the canal of Guyon. This study can also help in distinguishing distal entrap- ment syndromes from compression at or near elbow, because DUCN conduction would be expected to be abnormal or absent in the presence of lesions at or above elbow (Kim et al., 1981). Letter to the Editor Dorsal ulnar cutaneous neuropathy B. NAZLIEL, A. I . . BAYSAL and Y. BIÇER GÖMCELI Gazi University Faculty of Medicine, Department of Neurology, Ankara, Turkey ———— Table1 Ulnar Nerve Conduction (NC) Studies, Left Arm Nerve Conduction Amplitude Velocity (m/sec) (microvolt/ mV) Sensory NC DUCN NP Digit V-wrist 40.9 (37.3) 14.4 microvolt (7.0) Mixed NC Wrist-Elbow 61.8 (49.8) 10.0 microvolt (5.2) Elbow-Axilla 61.2 (48.2) 12.0 microvolt (8.6) Motor NC Distal latency (ms) 2.6 (3.3) 12.0 mV (7.0) Elbow-Wrist 68.7 (49.9) 12.0 mV (7.0) Elbow 57.11 (39.6) 12.0 mV (7.0) Axilla-Elbow 54.7 (52.0) 12.0 mV (7.0) *DUCN : Dorsal ulnar cutaneous nerve *NP : No potential obtained (**) : Numbers in parentheses represent normal values.