Neuromuscular Scoliosis

Neuromuscular scoliosis is a spinal deformity, usually a long C-shaped curve often with pelvic obliquity and sometimes kyphosis, that results from weakness, imbalance or loss of trunk control in a neurological or muscular disease. It differs from idiopathic scoliosis because it begins early, progresses fast, continues after skeletal maturity, and harms sitting, breathing and comfort.

It occurs in cerebral palsy (about 20 to 25% overall, and up to 60 to 75% of non-ambulant children), Duchenne muscular dystrophy (over 90% without long term corticosteroids, much less with them), spinal muscular atrophy (over 90% in children who never walk), myelomeningocele (60 to 90%, depending on the neurological level), Friedreich ataxia, Rett syndrome, Charcot-Marie-Tooth disease, and spinal cord injury in childhood.

Curves over 50 degrees continue to progress by about 1 to 2 degrees a year after maturity. Complications are loss of sitting balance, pressure injuries over the ischia and sacrum, pain, restrictive lung disease and recurrent chest infection, reflux and feeding difficulty, hip subluxation, and a heavy care burden.

Pathophysiology.

Weak or imbalanced trunk muscles cannot hold the spine upright against gravity, particularly in sitting. Spasticity, asymmetric tone and pelvic obliquity add asymmetric load on the growing vertebral plates (Hueter-Volkmann effect), producing wedging and a curve that increases at each growth spurt. In Duchenne muscular dystrophy, progression is rapid after the loss of walking.

A child who slumps in the wheelchair or leans on one arm, a rib hump, trunk shift, pelvic obliquity, skin redness or pressure sores, pain when seated, difficulty with feeding or breathing, and a need for more support. Curves may progress over months.

Examine in the sitting position and supine: curve flexibility, pelvic obliquity (fixed or flexible), hips (subluxation or dislocation, windswept posture), contractures, tone and spasticity, skin, nutrition (weight, albumin, muscle bulk), swallowing, cough and breathing pattern, seizures, and any intrathecal baclofen pump. In myelomeningocele, check the shunt function and the skin over the spine.

• Sitting (or supported standing) posteroanterior and lateral radiographs of the whole spine and pelvis: Cobb angle, kyphosis, pelvic obliquity, hip position. Traction or bending films show curve flexibility.
• MRI of the spine in atypical or rapidly progressing curves, and in myelomeningocele (tethered cord, syrinx, shunt malfunction).
• Pulmonary function: forced vital capacity (a value under 40% of predicted increases surgical risk, and a value under 30% is high risk but not an absolute contraindication), sleep study and blood gases when hypoventilation is suspected.
• Echocardiography and electrocardiogram (essential in Duchenne muscular dystrophy and Friedreich ataxia).
• Nutritional assessment (body mass index, albumin above 35 g/L, lymphocyte count above 1.5 x 10^9/L), bone density and vitamin D level, full blood count, clotting screen (and platelet count and function in children on valproate), and swallow assessment.

Differential diagnosis.

• Idiopathic and congenital scoliosis.
• Syndromic scoliosis (Marfan syndrome, neurofibromatosis).
• Progression from intraspinal pathology (syrinx, tethered cord, shunt malfunction).
• Hip pathology with pelvic obliquity, and spinal infection or tumour.

The aims are comfortable sitting, preserved breathing and a pain free trunk. Care is by a team of spine surgeon, neurologist, respiratory physician, anaesthetist, nutritionist and rehabilitation staff.

Non-operative care.

• Custom moulded seating and trunk supports, and a soft or rigid thoracolumbosacral orthosis for sitting support; a brace does not stop progression, and may impair breathing and be poorly tolerated.
• Physiotherapy, positioning, hip surveillance, pressure care, cough assistance and non-invasive ventilation when indicated, gastrostomy for failure to thrive or unsafe swallowing, and treatment of reflux.
• Duchenne muscular dystrophy: long term glucocorticoids (prednisolone 0.75 mg/kg daily or deflazacort 0.9 mg/kg daily, set by the neuromuscular team) reduce scoliosis and prolong walking; monitor growth, blood pressure, glucose, bone density and adrenal suppression.
• Bone health: correct vitamin D deficiency with colecalciferol 1000 to 2000 units orally daily, ensure a calcium intake of 1000 to 1300 mg daily; zoledronic acid 0.025 to 0.05 mg/kg intravenously (maximum 4 mg) every 6 months is used in specialist centres for low trauma vertebral or long bone fractures (check calcium and vitamin D first; watch for hypocalcaemia and an acute phase reaction).

Surgery (curves over 50 degrees with progression, sitting imbalance, pain or declining function; in Duchenne muscular dystrophy at 20 to 30 degrees while forced vital capacity is still over 30 to 40%).

• Posterior spinal fusion with segmental instrumentation (pedicle screws, sublaminar wires or hooks), extended to the pelvis (iliac or sacral alar iliac screws) when pelvic obliquity is over 15 degrees or the patient does not walk.
• Halo gravity traction before surgery for rigid curves over 90 degrees; growth friendly systems for young children.
• Complication rates are 20 to 50%: pneumonia, prolonged ventilation, deep infection (5 to 10%), pseudarthrosis, implant failure, ileus, superior mesenteric artery syndrome, pancreatitis, pressure injury, bleeding, and death in 1 to 3%.

Perioperative medication.

• Duchenne muscular dystrophy and other myopathies: avoid succinylcholine and volatile anaesthetic agents (risk of rhabdomyolysis, hyperkalaemia and cardiac arrest); use total intravenous anaesthesia.
• Long term glucocorticoids (3 weeks or more in the previous 12 months): hydrocortisone 2 mg/kg intravenously at induction (maximum 100 mg), then 1 mg/kg every 6 hours (maximum 50 mg a dose) for 24 to 48 hours, then the usual dose when eating.
• Antiseizure medicines continue without interruption; with valproate, check platelets and fibrinogen. Intrathecal baclofen continues without interruption (abrupt withdrawal causes fever, spasm, seizures and rebound spasticity); check pump function before surgery.
• Latex free environment for myelomeningocele.
• Cefazolin 30 mg/kg to a maximum of 2 g intravenously (2 g in adolescents) within 60 minutes before incision, repeated after 4 hours or blood loss over 1500 mL; add gentamicin 5 mg/kg intravenously once (check renal function; avoid in renal impairment) in some centres for patients with incontinence or gastrostomy; with severe penicillin allergy, vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose.
• Tranexamic acid 50 mg/kg intravenously over 15 minutes before incision, then 5 mg/kg/hour until wound closure (maximum 100 mg/kg in total, or 4 g); use with caution in poorly controlled epilepsy; avoid with a history of thromboembolism or active intravascular clotting.

Analgesia.

• Paracetamol 15 mg/kg orally or intravenously every 4 to 6 hours (maximum 75 mg/kg daily and not exceeding 4 g daily).
• Morphine by patient controlled or nurse controlled analgesia (bolus 10 to 20 micrograms/kg, lockout 5 to 10 minutes, maximum 0.3 mg/kg in 4 hours), then oral morphine 0.1 to 0.2 mg/kg every 4 hours as needed (maximum 10 mg a dose); reduce the dose in respiratory weakness and monitor with continuous oximetry; prescribe a laxative.
• Diazepam 0.05 to 0.1 mg/kg orally every 8 hours as needed for spasm (maximum 5 mg a dose) for up to 5 to 7 days; avoid with respiratory insufficiency or sleep apnoea unless monitored.
• Gabapentin 5 mg/kg orally at night (maximum 300 mg), increased to 5 to 10 mg/kg three times daily (maximum 900 mg three times daily; reduce at creatinine clearance under 60 mL/min) for up to 2 weeks.

Monitoring. Sitting radiographs every 6 months, annual or more frequent pulmonary function, nutrition and swallow, skin, hips, pump function, and cardiac review in Duchenne muscular dystrophy. After surgery, intensive care or high dependency monitoring, chest physiotherapy, early sitting, and review at 2 weeks, 6 weeks, 3 months, 6 months, 12 months and 24 months.

Referral and escalation. Refer any child with neuromuscular disease and a curve over 20 degrees (or progression of 10 degrees in a year) to a spinal service; surveillance of the spine should start early. Urgent referral for rapid progression, pressure injuries, falling lung function, or signs of shunt malfunction. Emergency referral for a new neurological deficit or wound infection after surgery.

Special groups.

• Spinal muscular atrophy: fusion may block access for intrathecal drug administration, so plan with the neuromuscular team (a laminotomy window may be left).
• Cerebral palsy: assess hips, spasticity treatment and nutrition; discuss goals of care with families.
• Myelomeningocele: shunt, tethered cord, skin, bowel and bladder care.
• Adults with progressive curves: monitor pain, skin and breathing.