Incidentally discovered monostotic Paget's disease involving the scapula inducing brachial plexopathy: A diagnostic dilemma.

Paget disease of bone is a chronic skeletal disorder characterized by abnormal bone remodeling. This condition, which predominantly affects older adults, can result in a variety of complications, including bone pain, fractures, and deformities. This case report discusses the incidental discovery of monostotic Paget's disease involving the scapula, leading to brachial plexopathy in a 58-year-old female with a history of colon cancer. The patient had severe bilateral shoulder pain, predominantly on the left, for the past ten years. This pain, exacerbated by overhead activity and limiting daily functions, radiated to the upper limbs without causing weakness or sensory deficits. Clinical examination revealed 4/5 limb power and normal sensation, with significant pain on left shoulder movement and limited elevation. Radiographic investigations, including bilateral shoulder radiographs, contrast-enhanced computed tomography (CT), and cervical magnetic resonance imaging (MRI), identified no displaced fractures but showed diffuse enlargement of left shoulder muscles with fatty infiltration, medullary expansion of the scapula, and reduced left lung volume. MDP skeletal scintigraphy with SPECT/CT confirmed asymmetrical radiotracer uptake and medullary expansion in the left scapula. Further, MRI of both shoulders revealed left-sided expansion, cortical thickening, and fatty replacement of the rotator cuff and deltoid musculature due to denervation pseudohypertrophy from left brachial plexopathy. The right shoulder MRI showed rotator cuff tendinopathy and tears. The findings suggest a diagnosis of monostotic Paget's disease with secondary brachial plexopathy.