Posterior interosseous neuropathy
The Posterior interosseous nerve (PIN) arises from the radial nerve; the radial nerve (RN) divides into a sensory branch and a deep motor branch, which pierces the supinator muscle. Trauma, tumours, compression or inflammation can cause lesions of the RN.
Symptoms such as ulnar wrist drop and finger drop are clinical manifestations of a PIN lesion. Elbow extension, complete wrist drop and supination weakness are symptoms related to a RN lesion. Neuroimaging and magnetic resonance neurography (MRN) can be used to diagnose these lesions.
The aim of this study was, to detect the location of the lesion of the PIN, and to be able to relate it to the spatial patterns using MRN.
It was initially thought that patients with an isolated finger drop have an entrapment neuropathy of the deep motor branch of the RN. However, this study provides evidence that neuroimaging is able to detect proximal lesions of the RN in the upper arm, and is frequently the cause of this clinical presentation.
Peripheral nerves do not have a high degree of longitudinal formation of their fascicles, which is a relevant implication in posterior interosseus neuropathy syndrome. Another important explanation is the amount of time that the patient has had the finger drop, especially in relation to diabetic patients.
The most important finding of this study is that neuroimaging can diagnose the cause of the finger drop and the exact location of the lesion can be determined. This is especially important for patients, who would have had surgery of the elbow. For physiotherapists it is important to realize that patients that have symptoms like a finger drop, can have a PN lesion as well as a proximal RN lesion.
> From: Bäumer et al., Neurology (2016) (Epub ahead of print). All rights reserved to American Academy of Neurology. Click here for the Pubmed summary.