Parsonage–Turner syndrome (PTS) is a rare neurological disorder that causes major diagnostic problems. This paper presents a case report of a patient with PTS and proposes a new physiotherapy program. Case description: a 23-year-old man presents a sudden severe pain of his right arm. The man is consulted by several doctors and physiotherapists. Three magnetic resonance imagings (MRI), a nerve conduction study (NCS), and needle electromyography (EMG) are performed. After 6 months, based on medical history, physical examination and ultrasound imaging (UI), the physiotherapist suggests PTS, which is confirmed by a neurologist. Intervention: due to the lack of physiotherapy treatment standards in PTS, we apply neurodynamic techniques. Outcomes: neurodynamic techniques are effective in reducing pain and paraesthesia, improving sensation, and reducing nerve swelling (assessed by UI), as well as improving manual dexterity and overall health status. Conclusions: the patient with PTS is challenging for making an accurate diagnosis. This study shows an important role for UI, which shows changes in the musculocutaneous nerve, despite the lack of abnormalities in the MRI, NCS, and EMG, and helps in making an accurate diagnosis. This report also confirms that physiotherapy based on neurodynamic techniques may have beneficial effects in PTS.