Charcot (Neuropathic) Arthropathy of the Shoulder

The defining feature of a Charcot shoulder is destruction out of proportion to pain: the joint is grossly swollen and disorganised, often unstable, yet relatively painless, because the underlying problem is loss of protective sensation and proprioception. The leading cause of an upper-limb neuropathic joint (elbow and shoulder) is syringomyelia, so a painless destroyed shoulder should prompt MRI of the cervical spinal cord to find a syrinx. The mechanism combines the neurotraumatic theory (unperceived repetitive microtrauma) and the neurovascular theory (autonomic dysregulation increasing bone resorption). Radiographs show resorption and fragmentation of the humeral head with bony debris - the disorganised 'bag of bones', summarised as the 6 Ds (Destruction, Density, Debris, Dislocation, Disorganisation, Distension).

The bedside sign that makes the diagnosis is the sensory pattern, not the joint. A cervical syrinx expands first through the crossing spinothalamic fibres in the anterior commissure, so it produces dissociated sensory loss - pain and temperature sensation are lost while light touch, vibration and proprioception are preserved - distributed over the shoulders and upper trunk in the classic "cape" or "shawl" distribution. Look also for wasting and weakness of the small muscles of the hand (anterior horn involvement) and lost upper-limb reflexes. A patient who cannot feel a pinprick over the shoulder but can feel light touch there has declared the cause of their destroyed joint.

Atrophic versus hypertrophic. Charcot joints take two radiographic forms, and the limb predicts which. The upper limb, and syringomyelic joints in particular, tend to the ATROPHIC pattern - pure osteolysis and resorption of the humeral head with little new bone, so the head appears to dissolve or be "licked" away. The hypertrophic pattern - exuberant sclerosis, osteophyte and periosteal new bone, the full 6 Ds - is more characteristic of the weight-bearing lower limb, as in the diabetic Charcot foot. Expect resorption at the shoulder and do not be reassured by the absence of florid new bone.

Syringomyelia is the classic upper-limb cause, but the joint distribution usually points to the underlying neurological disease (each cause is developed in its own topic).

• Exclude the dangerous mimics first. The grossly swollen, destroyed, fluid-filled shoulder can look like a tumour (an expansile mass) or infection (septic arthritis/osteomyelitis); image appropriately and, when there is doubt, aspirate and/or biopsy before attributing the destruction to neuropathy. Note that infection can coexist with a neuropathic joint rather than merely mimic it, so a raised inflammatory response does not exclude the diagnosis - and does not excuse skipping the aspirate.
• The other destroyed shoulder to know is Milwaukee shoulder - rapidly destructive cuff-tear arthropathy driven by basic calcium phosphate crystals, in an elderly patient with a large effusion and a massive cuff tear. It is distinguished by the absence of a neurological deficit and by pain that fits the destruction, whereas the Charcot shoulder is painless out of proportion (developed in our Milwaukee Shoulder and Rotator Cuff Arthropathy topics).
• Find and treat the underlying cause. Image the cervical cord (MRI) for a syrinx (often with a Chiari malformation); neurosurgical decompression may be indicated for a progressive syrinx.
• Largely supportive joint care. Protect the joint, manage symptoms and maintain function; activity modification and bracing have a role.
• Surgery is selective and unreliable. Charcot joints have high surgical complication and failure rates; arthrodesis is difficult and often fails, and arthroplasty is reserved for carefully selected cases, ideally after the neurological process is addressed, within a multidisciplinary team.