Pancoast syndrome, classically considered as a constellation of (1) pain along the C8–T2 dermatomes, (2) weakness and atrophy of the hand and (3) Horner's syndrome, often presents a diagnostic challenge. In fact, it may manifest as a singular orthopaedic complaint, prompting a futile barrage of tests and referrals. The authors present the case of an elderly man who initially presented with severe shoulder pain. Due to progressive pain and weakness, he was referred to rheumatology and was treated with corticosteroid injections for a presumed musculoskeletal lesion. Ultimately, he manifested gross muscular atrophy and worsening pain, prompting a referral to neurology. An electromyogram (EMG) suggested a lower brachial plexopathy, and a follow-up brachial plexus MRI identified a large Pancoast tumour. Unfortunately, his disease was rapidly progressive, and he passed away within 2 months. While the MRI remains the gold standard for diagnosing Pancoast syndrome, an EMG can facilitate diagnosis in difficult cases such as this one.