Neuropathic pain in children: SAQ

This girl has complex regional pain syndrome of the right lower limb. Her pain is disproportionate to the minor twisting injury, which has healed, and she has the characteristic features: allodynia, demonstrated by flinching on light touch and by her description that the bedsocks and bedclothes hurt, hyperalgesia, with the shower water feeling like needles, and regional autonomic and trophic change with the cool, pale, swollen foot. The Mesaroli five-year retrospective review and the broader literature establish that complex regional pain syndrome predominates in adolescent girls and affects the lower limb, and this girl fits that picture exactly. Her normal inflammatory markers and the absence of fever exclude a septic or inflammatory joint, which is the critical exclusion to make before diagnosing complex regional pain syndrome, and her normal structural neurological examination makes a compressive lesion unlikely. On the NeuPSIG grading system her pain is at least possible neuropathic pain, with a neuroanatomic distribution and a plausible injury, and the clinical picture is sufficient to begin the neuropathic plan. [9]

Question 1 (10 marks)

Outline your initial assessment and the foundation of your management plan for this girl, including the diagnosis and how you would exclude dangerous alternatives. [9]

My first task is to confirm the diagnosis and exclude the dangerous alternatives. The diagnosis of complex regional pain syndrome is clinical: severe regional pain disproportionate to any inciting event, accompanied by sensory changes such as allodynia and hyperalgesia, vasomotor changes such as colour and temperature difference, sudomotor changes such as swelling, and motor changes such as a reduced range of movement or dystonia. This girl has all of these, and the Mesaroli review confirms that this presentation in an adolescent girl with lower-limb involvement is the typical paediatric picture. [9]

The single most important alternative to exclude is infection. A warm, swollen, painful limb in a febrile or unwell child is septic arthritis or osteomyelitis until proven otherwise, and complex regional pain syndrome is a diagnosis of exclusion that must never be made in the face of fever or systemic illness. This girl is afebrile and well, and her inflammatory markers and full blood count are normal, which makes infection unlikely, but the exclusion is an active one and I would document the reasoning explicitly. I would also exclude a structural lesion of the nervous system through a deliberate red-flag screen: there is no progressive pain, no focal deficit, no sphincter disturbance, and no systemic features, and the neurological examination is normal, so urgent imaging is not required. The cool, pale limb is the autonomic dysregulation of complex regional pain syndrome, not vascular insufficiency. [9]

The foundation of the management plan is not a drug. The most important single intervention for complex regional pain syndrome is an intensive, function-focused exercise-based rehabilitation programme, and the classic series by Sherry and colleagues demonstrated excellent short- and long-term outcomes with exercise therapy. I would refer her urgently to physiotherapy for a graded programme of desensitisation, weight-bearing, and functional exercise, avoiding immobilisation because rest deepens the disuse and sensitisation that drive the syndrome. I would give a clear, mechanism-based explanation to the girl and her family: the nerve is misfiring and the brain has turned up the gain on the pain, the tissues are not being damaged, and the goal is to retrain the nervous system through movement. [6]

Because she has missed school and is sleeping poorly, I would add psychological support, with cognitive behavioural therapy to reframe the pain, reduce the fear of movement that drives disuse, and address the sleep and mood disturbance that amplify the nervous system's gain. I would quantify her disability with a validated paediatric pain and quality-of-life measure to track her response. I would counsel the family that the goal is a return to function rather than the abolition of pain, that the prognosis with early intensive rehabilitation is excellent, and that I would review her in clinic at two to four weeks with the physiotherapy team. [9]

Question 2 (10 marks)

Discuss the role, dosing, monitoring, and evidence base for pharmacotherapy in this girl, including the position you would take on gabapentin and amitriptyline. [3]

Pharmacotherapy is an adjunct to the rehabilitation and psychological plan, never a substitute for it. If this girl's pain remained severe enough to limit her participation in the exercise programme despite the foundation plan, I would consider adding a gabapentinoid, and gabapentin is the one most often used first in children. I would start it low, at about 10 mg per kg per day in divided doses, given initially as a single night-time dose to minimise sedation, and titrate over one to two weeks from once daily to twice daily to three times daily toward a usual effective range of 25 to 35 mg per kg per day in three divided doses, with doses up to about 40 to 50 mg per kg per day tolerated in some children. I would reduce the dose if her renal function were impaired, because gabapentin is excreted unchanged by the kidney, and I would warn the family that it must never be stopped abruptly because abrupt withdrawal can precipitate anxiety, insomnia, nausea, sweating, and seizures, even after a short course, and it is tapered over at least a week. I would monitor for sedation, dizziness, ataxia, and behavioural change, which are commonest during titration. [3]

Amitriptyline is the alternative I would consider where sleep disturbance and mood symptoms are prominent. I would obtain a baseline electrocardiogram before starting, because tricyclics prolong the QT interval and can cause conduction disturbance, and I would withhold the drug and consult cardiology if the QTc were prolonged. I would start at 0.1 to 0.2 mg per kg at night, often simplified to a fixed 5 to 10 mg at night for an adolescent, and titrate gradually over two to three weeks to a maximum of about 0.5 to 1 mg per kg per day, repeating the ECG after dose increases or if she reported palpitations, dizziness, or syncope. The anticholinergic effects of dry mouth and constipation and the morning sedation are the dose-limiting effects. [4]

I would be explicit with the family about the evidence base, because a fellowship-level answer must confront it. The 2017 Cochrane review by Cooper and colleagues found insufficient evidence to determine the efficacy and safety of antiepileptic drugs, including gabapentin, for chronic non-cancer pain in children and adolescents, and a parallel review found the same paucity of evidence for antidepressants. The GABA-1 trial by Kaguelidou and colleagues was established precisely because gabapentin was being used off-label in children without reliable evidence of its effects and optimal dosing. The drugs are used because the adult evidence supports them and because clinical experience is favourable, but they are used cautiously, off-label, and judged on function rather than on pain intensity alone. [3]

Two principles would govern my use of pharmacotherapy. First, I would never escalate opioids for this girl's neuropathic pain, because neuropathic pain responds poorly to opioids and the doses required carry a high risk of dependence, sedation, and opioid-induced hyperalgesia. Second, I would hold the goal as the return of function and school attendance, and I would wean any drug once that goal was met and the pain had settled, rather than continuing it indefinitely. [3]