A mimic of first dorsal interosseus atrophy revealed by ultrasound study

Clinical Neurophysiology xxx (2014) xxx–xxx Contents lists available at ScienceDirect Clinical Neurophysiology journal homepage: www.elsevier.com/locate/clinph Case Report A mimic of first dorsal interosseus atrophy revealed by ultrasound study Federica Ginanneschi ⇑, Georgios Filippou, Monica Ulivelli, Andrea Mignarri, Alessandro Rossi Department of Medical, Surgical and Neurological Sciences, University of Siena, Italy Ultrasonography (US) is becoming one of the most widely used diagnostic technique in neuromuscular diseases. It represents an ideal complementary tool that can enhance the accuracy of nerve conduction studies and needle electromyography (EMG) examination. Here we report the unusual case of seeming atrophy of first dorsal interosseous muscle (FDI) caused by thinning of the adductor pollicis muscle (AP). Differential diagnosis of FDI atrophy comprises ulnar neuropathy, lower trunk plexopathy, C8–T1 radiculopathy and spinal cord lesion, and degenerative disease such as amyotrophic lateral sclerosis. The patient was a 67-year-old female who had no history of any major disease. She presented with a three-year history of progressive weakness of thumb adduction and FDI atrophy (upper section Fig. 1). She never experienced hand numbness and the superficial sensory perception did not show changes in both hands. Nuclear magnetic resonance of the cervical spinal cord did not show any significant abnormalities. The motor nerve conduction studies performed with surface recording electrodes placed over the motor point of the abductor digiti minimi (ADM) and FDI muscles for the ulnar nerve and over the abductor pollicis brevis (APB) for the median nerve, standard needle EMG of FDI, ADM, and APB muscles, and the sensory conduction of the ulnar and median nerves were all normal. The dorsal and volar aspect of the first interdigital space of the left and right hands were studied by US. High-resolution US examination was performed using a real-time scanner with a 7–18 MHz linear array transducer. Ulnar nerve was followed along the entire length in the upper limb. Transverse and longitudinal views were obtained, without disclosing any abnormality. On the other hand, severe reduction of the AP muscle volume in the right hand was observed, while the FDI muscle volume was normal in both hands (lower section Fig. 1). EMG needle electrode was inserted under the guidance of US into the AP muscle which led to the detection of large amplitude motor unit action potentials with reduced recruitment patterns on volition. Ulnar nerve conduction parameters recorded by the same needle were obtained: compound muscle action potential amplitude was considerably reduced (1.9 mV) and motor conduction velocity was slightly and uniformly slowed without conduction block along the limb. The clinical and neurophysiological follow-up at six months did not show any change. ⇑ Corresponding author. Address: Department of Medical, Surgical and Neurological Sciences, Neurology-Neurophysiology Unit, University of Siena, Policlinico Le Scotte, Viale Bracci 1, 53100 Siena, Italy. Tel.: +39 0577 585769. E-mail address: ginanneschi@unisi.it (F. Ginanneschi). The AP is the deeper and more medial muscle of the thenar eminence. It is a flat, fleshy, triangular fan shaped muscle that overlies the metacarpal bones and the FDI. The gross innervation of adductor pollicis by branches of the deep ulnar nerve is widely accepted (Chang and Blair, 1985). In our patient, the atrophy of the AP may be related to a post traumatic damage of these small branches of the ulnar nerve before its termination in the FDI. A proximal fascic- Fig. 1. In the upper section, a photograph showing the asymmetry of the first dorsal interosseus muscle (FDI). Seeming atrophy of the FDI muscle in the right hand. In the lower section, ultrasonographic findings: dorsal (A, B) and volar (C, D) ultrasound scan at the first interdigital space of the right (A, C) and left (B, D) hand. AP: adductor pollicis muscle; FDI: first dorsal interosseus muscle. Note the severe reduction of the AP muscle volume in B and D. The FDI muscle volume is normal in both hands. http://dx.doi.org/10.1016/j.clinph.2014.05.006 1388-2457/Ó 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Please cite this article in press as: Ginanneschi F et al. A mimic of first dorsal interosseus atrophy revealed by ultrasound study. Clin Neurophysiol (2014), http://dx.doi.org/10.1016/j.clinph.2014.05.006 2 F. Ginanneschi et al. / Clinical Neurophysiology xxx (2014) xxx–xxx ular lesion of the ulnar nerve seems less likely, given the extreme selectivity of the muscle damage and the lack of nerve abnormalities at ultrasonographic study. The AP thinning caused the FDI to slip down out of his normal position, mimicking a FDI atrophy (upper section Fig. 1). This case report reveals that US plays an indispensable role in the diagnosis of neuromuscular diseases characterized by damage of nerves and muscles that are deeper and then more difficult to assess without direct ultrasound guidance (Hobson-Webb et al., 2012). Conflict of interest None of the authors have potential conflicts of interest to be disclosed. References Chang L, Blair WF. The origin and innervation of the adductor pollicis muscle. J Anat 1985;140:381–8. Hobson-Webb LD, Padua L, Martinoli C. Ultrasonography in the diagnosis of peripheral nerve disease. Expert Opin Med Diagn 2012;6:457–71. Please cite this article in press as: Ginanneschi F et al. A mimic of first dorsal interosseus atrophy revealed by ultrasound study. Clin Neurophysiol (2014), http://dx.doi.org/10.1016/j.clinph.2014.05.006