Hereditary neuralgic amyotrophy (HNA), also known as hereditary brachial plexopathy, is a rare disorder characterized by an acute onset of severe pain, palsy, amyotrophy and abnormal sensation, typically involving the shoulder girdle and upper extremities. The age of onset of HNA can range from early childhood to adulthood with a mean age of diagnosis of 28 years (van Alfen and van Engelen, 2006). Additional, non-neurologic features may be present in some individuals with HNA and can include hypotelorism, short stature, and cleft palate (Jeannet et al., 2001). Individuals may have recurrent episodes with symptom-free intervals.

SEPTIN9 (formerly referred to as the SEPT9 gene) is the only gene in which pathogenic/likely pathogenic (P/LP) variants are known to cause HNA; however, only about 55% of individuals with a clinical diagnosis of HNA are found to have a P/LP variant (Van Eijk et al., 2016). HNA is inherited in an autosomal dominant fashion. An idiopathic form of neuralgic amyotrophy (NA), also known as Parsonage Turner Syndrome, has a similar clinical presentation of the neurologic findings to HNA. Patients with HNA are more likely to have earlier onset and recurrent attacks, involvement of non-brachial sites, and more frequent disability due to multiple attacks (Seror 2016). The diagnosis of both NA and HNA is typically based on clinical findings, and genetic testing for SEPTIN9 is not a part of routine diagnostics (Burgunder, EFNS Guidelines 2011). 

Pain management is the foremost intention of therapy for both NA and HNA, and differs  between acute and chronic stages. Corticosteroids and discussion with a physiatrist is advised. After initial diagnosis, follow up every six to 12 months is recommended to identify chronic pain that may come from modified biomechanics of the shoulder or arm. Women with HNA should be watched in the post-partum period for the development of symptoms. Immediate treatment with corticosteroids or similar medications may lessen the symptoms of a HNA attack. Immunotherapy with intravenous immunoglobulins have also been used successfully to treat both NA and HNA (Chuk et al, 2016; Morishima et al., 2018). There is some suggestion that there may be different recommendations in the use of surgery for the treatment of NA versus HNA, but the literature is not in agreement and randomized trials are needed to establish efficacy of standardized treatment for both conditions (Van Alfen 2009, Seror 2016).