MSK for Tuesday, April 8th, 2025

History

A six-year-old child with a history of congenital insensitivity to pain presented to the pediatric emergency room with complaints of acute on chronic left ankle swelling. Approximately three months prior, she had broken her left tibia which was treated with casting for seven weeks. Upon removal of the cast, the patient had persistent swelling in her left ankle with increasing swelling at the heel. She was seen by orthopedics again with repeat radiographs concerning for healing fracture of the calcaneus. MRI was then performed.

Patient was afebrile with stable vital signs. C-reactive protein was mildly elevated, ranging from 4.5 to 5.7 mg/L. 

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Question

What is the diagnosis?

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Correct answer

Charcot arthropathy

Discussion

Differentiating osteomyelitis from neuropathic arthropathy can be difficult with imaging alone and clinical context is often key. In this patient, the history of congenital insensitivity to pain is paramount to the correct interpretation of imaging findings. Congenital insensitivity to pain (CIP) refers to a rare genetic syndrome typically manifesting from mutations related to pain signaling pathways. The patient presented here has a known mutation in the NTRK1 gene on chromosome 1 which codes for a receptor tyrosine kinase for nerve growth factor, with mutations resulting in abnormal nociceptive function (1). In this clinical setting, repeated trauma and injury to the joint in the absence of pain perception can result in neuropathic or Charcot arthropathy. Initial presentations may be nondescript with joint swelling or erythema, with the absence of related pain a distinguishing characteristic, particularly if a diagnosis of CIP has not already been established. 

Radiographic features are often nonspecific early in the disease process, however destructive changes including fragmentation with or without dislocation can be seen. MRI features of neuropathic joint-related processes can vary depending on the stage of disease, however, generally include abnormal bone marrow signal, soft tissue edema, joint effusions, subchondral fractures, bone debris, and formation of intra-articular bodies (2–4). Often, the earliest manifestation is marrow edema. Later in the disease additional features can include productive bone changes and the potential for disorganized joint dislocation or subluxation. In the ankle and foot, this often manifests in later stages with midfoot collapse and can result in pes planus or in end-stage cases even rocker-bottom feet (2,5). Radiography is a useful imaging tool for initial diagnosis; however, MRI can provide early findings not seen on radiographs or CT and can be useful in problem solving, particularly if infection is clinically suspected. Importantly, these injuries may be more rapidly progressive in the pediatric population due to the higher activity levels in children. Management will be dependent upon the severity and stage of the process, centered around preventing additional injuries and mitigating complications such as fractures and infection.

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References

• Indo Y. Molecular basis of congenital insensitivity to pain with anhidrosis (CIPA): mutations and polymorphisms in TRKA (NTRK1) gene encoding the receptor tyrosine kinase for nerve growth factor. Hum Mutat. 2001;18(6):462-471. doi:10.1002/humu.1224
• Rosskopf AB, Loupatatzis C, Pfirrmann CWA, Böni T, Berli MC. The Charcot foot: a pictorial review. Insights Imaging. 2019;10(1):77. doi:10.1186/s13244-019-0768-9
• Cassidy RC, Shaffer WO. Charcot arthropathy because of congenital insensitivity to pain in an adult. Spine J. 2008;8(4):691-695. doi:10.1016/j.spinee.2007.04.005
• Dardari D. An overview of Charcot’s neuroarthropathy. J Clin Transl Endocrinol. 2020;22. doi:10.1016/j.jcte.2020.100239
• Marmolejo VS, Arnold JF, Ponticello M, Anderson CA. Charcot Foot: Clinical Clues, Diagnostic Strategies, and Treatment Principles. Am Fam Physician. 2018;97(9):594-599.