As well as affecting the brachial plexus, Parsonage Turner syndrome can also affect nerves external to the brachial plexus during an acute episode.
In Nens van Alfen, 2006 study of 246 patients with Parsonage Turner syndrome1; 17.3% patients had involvement of nerves outside the brachial plexus; involving the lumbosacral plexus (8.2%), phrenic nerve (6.6%); recurrent laryngeal nerve (2%). There would also be combinations of nerve involvement. These proportions were much higher in patients with Hereditary form of Parsonage Turner Syndrome (55.8% overall).
References
1. Nens van Alfen & Baziel G. M. van Engelen. The clinical spectrum of neuralgic amyotrophy in 246 cases, Brain, 2006, 129, 438–450. https://doi.org/10.1093/brain/awh722
2. Nens van Alfen, Jonne Doorduin, Marieke H.J. van Rosmalen, Jeroen J.J. van Eijk, Yvonne Heijdra, Andrea J. Boon, Michael A. Gaytant, Ries J.M. van den Biggelaar, Roy T.M. Sprooten, Peter J. Wijkstra, Jan T. Groothuis Phrenic neuropathy and diaphragm dysfunction in neuralgic amyotrophy.Neurology Aug 2018, 91 (9) e843-e849; https://www.doi.org/10.1212/WNL.0000000000006076
3. Holtbernd F, am Zehnhoff-Dinnesen A, Duning T, Kemmling A, Ringelstein E, B: An Unusual Case of Neuralgic Amyotrophy Presenting with Bilateral Phrenic Nerve and Vocal Cord Paresis. Case Rep Neurol 2011;3:69-74. https://www.doi.org/10.1159/000325061