"Posterior interosseous nerve syndrome will often have an insidious onset, presenting with weakness of the wrist and digital extensors. Active wrist extension will often result in radial deviation, due to preservation of the extensor carpi radialis longus, which is supplied by the radial nerve. This entity is usually painless, and patients with an isolated posterior interosseous nerve syndrome will not have a sensory deficit. This clinical feature is useful in distinguishing this syndrome from radial tunnel syndrome."
"Imaging diagnosis based primarily on muscle denervation pattern; abnormal signal intensity or atrophy in muscles innervated by posterior interosseous nerve 4. MRI can also be used to identify any extrinsically compressive lesions, evaluate potential compression sites, and ultimately for surgical planning if intervention is appropriate."