P32-F Nerve ultrasound in the assessment of posterior interosseous nerve syndrome: a useful tool?

Background Nerve ultrasound (NUS) is a technique recently introduced in the routine assessment of neuromuscular diseases. In carpal tunnel syndrome adding a morphological test to the routine electrophysiological assessment does not increase neither cost nor excessive time to the exam. However, there is an ongoing debate if this kind of studies should be introduced in the neurophysiology laboratory and be performed by a neurophysiologist. Material and methods We present a case in which performing NUS at the same appointment as electromyography (EMG) and neurography implied a change in diagnosis and treatment. A 55-year-old male subject was scheduled for EMG and nerve conduction studies (NCS) due to an acute wrist drop following a 30 min nap. An acute compression of the radial nerve was suspected and EMG and NCS were performed to identify a possible radial mononeuropathy and exclude abnormalities in other nerves, plexus or roots. Results It was identified a pure motor lesion distal to triceps innervation, indicating a posterior interosseous nerve (PIN) syndrome. Additionally, a NUS exploration of the median, cubital and radial nerves was performed, and a hypo-anechoic mass was identified close to the supinator muscle and in contact with the PIN. A magnetic resonance imaging (MRI) was performed confirming previous findings. Conclusions This case is interesting because it depicts not only an infrequent entrapment neuropathy, namely posterior interosseous nerve syndrome, but also the added value that an easily available morphological study in a neurophysiology laboratory could have.