Nosology of idiopathic phrenic neuropathies

Phrenic neuropathies (PN) are an important cause of dyspnoea, orthopnoea and hypercapnic respiratory failure. However, there is no agreement on the nosology of this disorder. The aim of this cohort study was to analyze the author’s and published PN patients and compare them with other immune-mediated focal neuropathies to determine the most appropriate nomenclature and classification of the disorder. All patients with PN referred to the author from March 2004 to March 2013 were included. In addition, to identify previously published patients with PN, a PubMed search was done. The demographic and clinical characteristics of both series were then compared with the published series of neuralgic amyotrophy (NA) patients. Of 19 PN patients from the author’s series, 11 % fulfilled the criteria for definite and 58 % for probable NA; while in 58 previous patients, the values were 16 and 48 %, respectively. PN and NA both have a male preponderance and a frequent history of preceding events, but PN occur in an older population and more often in diabetics, are less commonly associated with pain, and have a less complete recovery. Although demonstrating some similarities with NA, the high proportion of isolated (particularly bilateral) PN point to a probable immune-mediated attack against some phrenic nerve-specific antigen with occasional spill-over to neighboring nerves. As a consequence, idiopathic PN seems to be more appropriately regarded as a distinct entity within the spectrum of immune-mediated focal neuropathies rather than as a variant of NA.