Neurosurgical Treatment of Cerebral Palsy

Abstract

There is a broad range of alternatives in terms of cerebral palsy treatment (intrathecal baclofen (ITB), selective dorsal rhizotomy (SDR), and deep brain stimulation (DBS)). In order to reduce dystonia and spasticity, ITB bump insertion, SDR, and DBS are the main neurosurgical treatment approaches. In ITB treatment, a baclofen pump is implanted in the abdomen and is connected to spine via a thin tube. The pump is refilled regularly. It may require a replacement surgery. SDR includes cut of sensory nerves in affected site. Globus pallidus is the target in DBS surgery, the main advantage of this technique is that, it is reversible and adjustable. In this chapter, neurosurgical treatment alternatives for cerebral palsy will be discussed.

1. Introduction

The International Executive Committee for Cerebral Palsy (CP) proposed the following definition: “Cerebral palsy describes a group of permanent disorders of the development of movement and posture, causing activity limitation, that are attributed to non-progressive disturbances that occurred in the developing fetal or infant brain. The motor disorders of CP are often accompanied by disturbances of sensation, perception, cognition, communication and behavior, by epilepsy, and by secondary musculoskeletal problems” [1]. This definition is supplemented by an interpretation of the terms used in the definition. CP can be defined according to the anatomical location of the brain lesion (cerebral cortex, pyramidal tract, extrapyramidal system, or cerebellum); clinical signs and symptoms (spasticity, dyskinesia [dystonic and choreo-athetotic forms], or ataxia); topographical involvement of extremities (diplegia, hemiplegia, or quadriplegia); timing of presumed insult (prepartum, intrapartum, or postneonatal); and classification of degree of muscle tone (isotonic, hypotonic, or hypertonic) [2]. Hypertonia, which is characterized by abnormal resistance to joint movement, is common in CP [2]. Spasticity, dystonia, rigidity or mixed subtypes are particular forms of hypertonia. Spasticity is the most common form of hypertonia, which is characterized by increased resistance to motion above a threshold joint speed [2]. The efferent output of alpha motor neurons regulates the muscle tone [3]. Dystonia is involuntary muscle activation causing abnormal posturing. Rigidity is resistance to motion independent from velocity, caused by simultaneous contraction of agonists and antagonist muscles. Treatment of CP targets the particular pathophysiology. In general, spasticity can be easier to manage than dystonia [4]. Studies on the management of spasticity are more abundant than those related to the management of dystonia in patients with CP.

There is an inverse relationship between the level of spasticity and voluntary motor control. In children with poor selective motor control, the spasticity can have functional importance (i.e. for standing). Treating this functional muscle tone may debilitate the child in everyday life [4]. Spasticity impairs selective motor control and treating it increases functionality.

The non-surgical treatment of CP includes enteral or intramuscular pharmacological agents, botulinum toxin injections, and physiotherapy [5]. When maximum tolerated dosage has been tried, neurosurgical alternatives such as intrathecal baclofen (ITB) therapy, selective dorsal rhizotomy (SDR), and deep brain stimulation (DBS) can be performed for the management of spasticity, muscle tone, and pain. The aim of neurosurgical interventions includes improvement in gross motor function, walking, muscle tone, health related quality of life, reduction of pain, and reducing the use of concurrent medication. In this chapter, we will review these procedures and provide up-to-date findings regarding neurosurgical alternatives in the management of hypertonia in CP.

2. Intrathecal baclofen pump

Intrathecal baclofen pump placement is a cost-effective treatment modality in spasticity and dystonia management of patients with CP that are non-responsive to enteral pharmacological treatments [6]. Penn and Kroin were the first scientists using ITB to treat spasticity in patients with multiple sclerosis [7]. Baclofen is a chlorophenol derivative of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) [3]. Intrathecal administration of this product results in ten times the concentration after oral administration [3]. Direct administration of baclofen to central nervous system via intrathecal route minimizes dosage and decreases systemic side effects when compared with oral form of baclofen [6]. ITB disseminates into the superficial layers of the spinal cord and binds to GABA_b receptor sites, and acts presynaptically. It inhibits the uptake of calcium and inhibits the release of excitatory neurotransmitters (i.e. glutamic acid and aspartic acid) [3]. A single dose of ITB reduces lower extremity muscle tone within 20–40 min, its maximum effect is seen in 4 h after administration. Its half-life is 5 h and a single dose is effective for 8–10 h. ITB treatment improves muscle tone, gait, and quality of life of patient with CP. Approximately 300 μg/day dose of ITB is mostly adequate in reducing lower extremity spasticity and diminishing muscle spasms [3]. ITB overdose results in coma, respiratory depression, and hypotonia [3]. These effects usually subside within 2–3 days. Intravenous physostigmine is the treatment of choice in ITB overdose, however severe overdoses are not reversed.

Continuous ITB is best achieved via a pump which delivers baclofen to the lumbar area of the spinal cord to reduce spasticity in the lower extremities [8]. The catheter is inserted through means of a 14-gauge Tuohy needle and enters the spinal canal at about L2, and the tip of the catheter is advanced to T10 for paraplegics, T5 for quadriplegics, and C5-T1 for complex movement disorders and dystonia [9]. Right lower quadrant of the abdomen is the usual side for subcutaneous pump placement. A catheter is passed from the pump into the intrathecal space. Baclofen dose can be arranged via a radiofrequency wand which transmits information from a computer to the implanted pump [10]. Test dose is needed in the preimplantation period before the procedure. This will help physician to assess the potential effects of baclofen on symptoms and function. The initial continuous infusion dose is mostly twice the single ITB dose that shows a clinically prominent effect. The daily dose is slowly increased until desired clinical effects are present. Regular follow-up and percutaneous pump refill every three to six months is a requirement for this procedure. The pump is refilled by inserting a needle through the skin into the reservoir. Frequent monitoring and dose adjustment is a must after pump placement. Pump replacement is also a necessity at the end of battery life (4–6.5 years). The pump is similar to hockey pump, and the child must weigh approximately 15–18 kg to accommodate the pump. ITB affects both spasticity and dystonia and benefits both ambulatory and non-ambulatory children.

Shared decision-making between physician and patient and his/her caregivers is an important step. The adverse events include CSF leakage, infection, catheter disconnection or breakage, constipation, respiratory depression, baclofen withdrawal, and baclofen overdose [5, 10]. Highest complications rates for ITB therapy are around 36% [11]. Baclofen withdrawal symptoms include muscle spasms, dysesthesias, pruritus, agitation, and rhabdomyolysis. Treatment of this issue is restoring the ITB delivery [6]. Contraindications are baclofen sensitivity, inappropriate body size for reservoir placement, non-compliant patient, or any limitation that inhibits close follow-up. In patients with unilateral spasticity, ITB would probably also decrease muscle tone on the healthy side and ITB is not recommended for these patient group. Benefits and risks associated with ITB treatment should be cautiously evaluated; individual needs, expectations, and clear treatment goals should be agreed before procedure. Children with moderate to severe spasticity spectrum will benefit from ITB.

3. Rhizotomies

3.1 Selective dorsal rhizotomy

Normal cerebral inhibitions of the monosynaptic reflex arc at the spinal cord level are lost in children with spasticity from CP. This results with spasticity or hyperreflexia. Spasticity can be diminished via disrupting this hyperactive monosynaptic reflex arc [8]. At the dorsal root level, selectively transecting the afferent sensory fibers can significantly decrease spasticity. After lumbar laminectomy, the dorsal rootlets are localized in the cauda equina. Lumbosacral spinal sensory nerve rootlets with abnormal thresholds to electromyographic stimulation are sectioned to solve the sensory dysfunction in spasticity [6]. These are the afferent dorsal rootlets that terminate on relatively uninhibited alpha motor neurons [3]. When sectioned, spasticity can be relieved without losing other functions of dorsal roots. An abnormal response is considered when a muscle, not typically innervated at that root level, responds or when several muscle groups respond simultaneously [8]. Usually, 50% of the rootlets are cut [12]. The percentage of rootlets cut does not necessarily correspond to the level of spasticity or severity of neurologic involvement. Following the rhizotomy, there is a temporary weakness which returns to normal in few months. The other risks for this procedure are loss of bladder and bowel control, sensory loss, wound infection and meningitis, and finally leakage of the spinal fluid through the wound. Best candidates for SDR are children with spastic diplegia, ambulatory, pure spastic, cognitively intact, and with good social structure [8]. SDR only resolves spasticity with no effect on dystonia. Children with quadriplegic CP may not benefit from SDR because of their significant dystonia. Contraindications are spasticity of spinal cord origin, athetosis, rigidity, history of previous tendon release/lengthening, poor trunk control, severe weakness.

Selective dorsal (posterior) rhizotomy is a costly, irreversible complex neurosurgical procedure to reduce muscle tone in patients with CP. There is concern for muscle weakness, spinal deformity, and need for additional orthopedic procedures. Evaluation of multidisciplinary team when deciding to perform SDR is a must. Birth history, neuroimaging, strength, selective motor control, gait analysis, and presence of fixed deformities should be considered beforehand [13]. This procedure should be reserved for the patient population who does not respond or tolerate the pharmacological treatments and meet specific selection criteria. Also this procedure should be performed by a specialist multidisciplinary team with expertise in the management of spasticity. Intensive physiotherapy is mostly required for several months after procedure because the sensory input is reduced to sensory-motor reflex arcs in the spinal cord. Walking ability may be disrupted and different walking skills may be needed after the procedure.

Long-term follow-up studies report that SDR is well-tolerated over the years and improves functional outcomes and quality of life [13, 14, 15]. Daunter et al. reported less decline in gross motor function and required less hours of assistance in daily activities, however there was no difference for pain and fatigue [16]. Munger et al. reported improved gait quality in ten-year follow-up study [17]. In that study, non-SDR group required more orthopedic interventions and injections. Quality of life or functional and mobility measures did not differ among SDR and non-SDR groups.

3.2 Ventral rhizotomy

In the presence of mixed tone, ventral rhizotomy (VR) may be performed in conjunction with SDR when there is limited access to ITB and DBS [6]. SDR inhibits the sensory dysfunction leading to spasticity, while VR aims to solve the motor abnormalities associated with dystonia. Using this procedure in diplegic/quadriplegic children with CP with mixed spasticity and dystonia, [18] reported improved joint range of motion, spasticity, and dystonia at one-year follow-up. Functional intraoperative monitoring is crucial for identifying the roots to preserve sphincter innervation. This combined intervention may have promise in children with severe mixed hypertonia.

4. Deep brain stimulation

Deep brain stimulation may also be indicated in patient that are not responsive to ITB therapy [19]. Electrodes are placed in the basal ganglia and connected to an implanted pulse generator. Basal ganglia and thalamocortical network modulation are targeted. The stimulation can be unilateral or bilateral [9]. In a study targeting internal globus pallidus, there was 33% reduction in dystonia measures at one-year follow-up [20]. Parkinson disease and congenital dystonia are 2 movement disorders with very good outcomes from DBS. Acquired dystonias, from CP and after brain injury, are very heterogeneous lesions, isolated excellent results have been obtained with DBS in those cases, but criteria for patient selection remain uncertain [9]. DBS is reserved for patients with significant functional limitations who failed all other interventions for severe generalized dystonia [21, 22, 23].

5. Discussion

Cerebral palsy is characterized by motor dysfunction due to lesion occurring non-progressive disorders of posture and movement caused by injury to the infant or developing fetal brain [1]. Neuromuscular and musculoskeletal problems such as spasticity, dystonia, muscle contractures, abnormal bone growth, poor balance, weakness, and loss of selective motor control are some of the main problems encountered by the patients with CP. Physical and occupational therapy, bracing, oral medications, neurolytic blocks, neurosurgical procedures, orthopedic surgery, and others are the treatment alternatives [4]. These modalities do not cure the disease but improve function and improve quality of life. A multidisciplinary team should evaluate the patient and optimize the treatment. Neurosurgeons also play an important role in this team. Focal spasticity can be treated via lesioning the nerve target [24]. ITB therapy is the first choice in patient that are not responsive to enteral and physical treatments. Ambulatory children with spastic diplegia and good cognitive abilities can be treated with SDR. In a non-functioning limb, dorsal root entry zone lesioning could be an option for severe cases. DBS can be effective in the treatment of primary dystonias (especially those caused by DYT-1 gene mutation [25].

The evidence for recommending neurosurgical procedures (ITB pumps and SDR) is limited and of low quality [5, 26]. Recommendation of these procedures depend on the experience and expertise of the multidisciplinary team. It should be a shared decision-making between surgeon, patient and caregiver. Reported adverse events for ITB pump are catheter or pump infections, battery failure, catheter leakage, baclofen withdrawal or overdose, constipation, anxiety or depression, and seizures. These modalities are considered as complex and invasive. There is a need for high quality evidence for the neurosurgical treatment of CP. Clear expectations and open treatment aims should be discussed before the final decision step.

6. Conclusion

Neurosurgical procedures (ITB, SDR, and DBS) are invasive and costly procedures for the treatment of hypertonia in patients with CP. These modalities are not preferred in the first stage of treatment selection. However, they are considered a second step options for non-responsive patients with CP to other treatments modalities because they improve the major symptoms related to CP. These procedures are accepted as risky but in well-selected cases these modalities could have a real impact on patient’s quality of life. High quality randomized controlled clinical trials are necessary to recommend these procedures for selected cases.

Conflict of interest

“The authors declare no conflict of interest.”