Knee MRI showing thickened peripheral nerves in Charcot–Marie–Tooth disease

A 16-year-old boy with 3-year history of knee pain was initially seen in the orthopedic clinic. He was then referred to the pediatric neurology clinic after an abnormal magnetic resonance imaging (MRI) of the knee (Figs. 1, 2). Axial and sagittal T2 weighted with fat suppressed MRI images obtained at the level of midline patella demonstrated diffuse enlargement of the sciatic (solid arrow) and tibial (dotted arrow) nerves with increased signal intensity. The knee joint was normal on MRI. On examination, the significant clinical findings were thoracic scoliosis, pes cavus, weakness of ankle and toe dorsiflexors, generalized areflexia, distal sensory loss in the legs and thickened peripheral nerves. The family history was negative for any neuromuscular disease or foot deformities. Electrodiagnostic studies were consistent with hereditary demyelinating sensorimotor polyneuropathy. DNA analysis identified the duplication of peripheral myelin protein 22 (PMP22) gene on chromosome 17. This confirmed the diagnosis of Charcot–Marie–Tooth (CMT) type 1A disease. CMT is a genetically heterogeneous group of inherited neuropathies with variable age of presentation [1]. The typical clinical presentation is that of slowly progressive distal lower extremity weakness and peroneal muscles atrophy with characteristic foot abnormalities (pes cavus, hammer toes), followed by weakness and atrophy of upper extremity muscles and sensory loss [2]. Genetically CMT type 1A is the most common form and is associated with 1.4 Mb duplication at chromosome 17p11.2 [1]. The family history may be negative in autosomal recessive or potentially new dominant mutations as noted in our case. In our patient the clinical features, electrodiagnostic studies and genetic studies confirmed CMT type 1A. However, the patient’s presentation with knee pain was atypical. We think that the knee pain was secondary to the foot deformities and muscle weakness due to CMT.