CRPS - Clinical Scenario

The patient’s history strongly supports a diagnosis of CRPS. The onset of pain following trauma (a distal radius fracture), which is disproportionate to the original injury, is a hallmark of CRPS.

The persistence of pain beyond the expected healing period and the presence of allodynia (pain from normally non-painful stimuli, such as light touch) further support the diagnosis.

Additionally, her reports of swelling, color changes, and sweating abnormalities indicate autonomic dysfunction, which is common in CRPS. The patient’s history of osteoporosis and migraines are recognized risk factors for CRPS, making this diagnosis more likely.

On physical examination, I would expect to find signs of sensory abnormalities such as allodynia (pain with light touch) and hyperalgesia (exaggerated pain with pinprick or pressure).

Autonomic changes may be observed, including temperature asymmetry (e.g., warmer or colder hand compared to the unaffected side), skin colour changes (pallor or redness), and sweating abnormalities (increased or decreased sweating).

In more advanced cases there may be:

• Trophic changes may include brittle nails and altered hair growth.
• Motor dysfunction, including reduced range of motion, weakness, and possibly tremor or dystonia.

Given the history of trauma, the presence of disproportionate pain, sensory and autonomic changes, and the chronicity of symptoms, CRPS is the most likely diagnosis. It fits the clinical picture as described and is supported by the patient’s risk factors (osteoporosis, migraines). Other differentials to exclude are:

1. Peripheral neuropathy: This would cause sensory changes but usually follows a dermatomal pattern, which is not seen here.
2. Infection (e.g., osteomyelitis or cellulitis): These conditions could explain swelling and redness but would typically present with systemic signs like fever and would not explain the degree of allodynia or hyperalgesia.
3. Deep vein thrombosis (DVT): Swelling and discoloration may be present, but DVT would not account for the severe pain, sensory changes, or motor dysfunction.
4. Arthritis (rheumatoid or osteoarthritis): Could explain joint pain and stiffness but would not present with the profound sensory and autonomic abnormalities.

The diagnosis of CRPS is primarily clinical, based on the Budapest Criteria. However, certain investigations can support the diagnosis or rule out other conditions:

1. Thermography: Can demonstrate temperature asymmetry, supporting the diagnosis of CRPS.
2. Bone scintigraphy: May show increased uptake in the affected region, which is sometimes seen in early CRPS.
3. Plain radiographs: To rule out any missed fractures or joint pathology and may show patchy osteoporosis in late-stage CRPS.
4. Electromyography (EMG): To rule out peripheral neuropathy.
5. Blood tests (e.g., inflammatory markers, full blood count): To rule out infection or inflammatory arthropathy.
6. MRI: Can assess for bone marrow edema, which may support the diagnosis of CRPS.

The Budapest Criteria require:

• A. Continuing pain disproportionate to the inciting event.
• B. At least one symptom in three of the four categories: sensory (hyperalgesia/allodynia), vasomotor (temperature/color asymmetry), sudomotor (edema or sweating changes), motor/trophic (weakness, decreased range of motion, trophic changes)
• C. At least one sign in two or more of the following categories: sensory (hyperalgesia/allodynia), vasomotor (temperature/color asymmetry), sudomotor (edema/sweating changes), motor/trophic (weakness/trophic changes)
• D. No other diagnosis better explains the symptoms.

In this case, the patient fulfills criteria A and B, with ongoing pain disproportionate to her injury, sensory (allodynia), vasomotor (temperature asymmetry, color changes), and sudomotor symptoms (sweating). Examination findings confirm signs in the sensory, vasomotor, and motor/trophic categories.

The initial management for CRPS should be multidisciplinary, aiming to reduce pain and improve function:

1. Physical and occupational therapy: Early mobilization with a focus on desensitization exercises, range of motion, and strengthening exercises to prevent further stiffness and muscle atrophy.
2. Pharmacological management: Starting with non-steroidal anti-inflammatory drugs (NSAIDs) for pain relief, followed by gabapentinoids (e.g., gabapentin or pregabalin) or tricyclic antidepressants (e.g., amitriptyline) to target neuropathic pain. Bisphosphonates could be considered due to her osteoporosis and their potential benefit in CRPS.
3. Psychological support: Given the chronic nature of CRPS, cognitive-behavioral therapy (CBT) is important to address the psychosocial burden of the disease.
4. Sympathetic blocks: If conservative measures fail, sympathetic blocks (e.g., stellate ganglion block) could be considered to modulate pain.

If conservative management fails, the following surgical options may be considered:

1. Dorsal root ganglion (DRG) stimulation: This targets pain relief by modulating the pain signals at the level of the spinal ganglion and is shown to be effective in CRPS.
2. Spinal cord stimulation (SCS): Used in refractory cases to reduce pain and improve function, by providing electrical stimulation to the spinal cord to modulate pain signals.
3. Surgical sympathectomy: In rare, refractory cases, surgical sympathectomy may be considered to disrupt the sympathetic pathways contributing to pain, although this is controversial and generally reserved for CRPS type II. Surgical intervention should be carefully considered in patients who have exhausted all other options, as the prognosis can be variable.

Untreated or chronic CRPS can lead to several complications:

1. Dystonia: Involuntary muscle contractions, often leading to abnormal posturing of the affected limb.
2. Chronic pain: The pain may become intractable and resistant to standard treatments.
3. Trophic changes: Irreversible skin, hair, and nail changes, as well as muscle wasting.
4. Psychological impact: Anxiety, depression, and reduced quality of life are common due to chronic pain and disability.
5. Functional impairment: Persistent stiffness, reduced range of motion, and weakness can result in significant functional loss.

Management of dystonia in CRPS includes:

1. Physical therapy: Targeting spasticity and maintaining range of motion.
2. Medications: Baclofen or botulinum toxin injections may help relieve dystonia.
3. Neuromodulation: If dystonia becomes severe, DRG stimulation or SCS may be beneficial. Prevention strategies include early and aggressive treatment of CRPS, regular physiotherapy to prevent contractures and stiffness, and addressing the psychosocial impact to prevent depression and anxiety, which can exacerbate pain.

Allodynia and hyperalgesia in CRPS are due to peripheral and central sensitization mechanisms.

In the peripheral nervous system, nociceptor sensitization occurs due to the release of pro-inflammatory mediators such as TNF-α and prostaglandin E2, which lower the pain threshold and increase the response to stimuli.

In the central nervous system, there is increased excitability of dorsal horn neurons, facilitated by neuropeptides like glutamate and substance P. This leads to abnormal amplification of pain signals (central sensitization), causing hyperalgesia and allodynia, where even non-painful stimuli, like light touch, are perceived as painful.

The sympathetic nervous system plays a critical role in the pathophysiology of CRPS through abnormal coupling between adrenergic and nociceptive neurons. This leads to increased pain following sympathetic activation, known as sympathetically maintained pain.

Treatment strategies targeting the sympathetic nervous system, such as sympathetic nerve blocks or sympathectomy, aim to disrupt this pathological coupling and reduce pain. Neuromodulation therapies like spinal cord stimulation also target sympathetic dysfunction by modulating abnormal pain processing at the central level.