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INTRATHECAL BACLOFEN INFUSION DEVICES

Generalized dystonia occurs in 15% to 25% of patients with cerebral palsy. Baclofen, a γ-aminobutyric acid agonist that acts at the level of the spinal cord by impeding the release of excitatory neurotransmitters, decreases spasticity. Oral baclofen offers patients only mild relief because of its inability to cross the blood–brain barrier and its poor lipid solubility. Intrathecal administration (Figure 175–9) is more effective, requires lower dosages, and leads to higher CSF levels. Intrathecal baclofen reduces spasticity and improves gait, sitting ability, and upper extremity function in most patients.29 Intrathecal baclofen pumps are also used to treat spasticity related to spinal cord injury, multiple sclerosis, brain injury, cerebrovascular accidents, and perinatal infection sequelae.29,30 Complications observed in patients receiving continuous intrathecal baclofen can be divided into medication-related, mechanical, and infection-related complications and are listed in Table 175–4.

Table 175–4

Complications of Intrathecal Baclofen Infusion

When a complication occurs disrupting the administration of baclofen, withdrawal symptoms can be severe and life-threatening, including extreme hypertonicity and spasms that may lead to rhabdomyolysis. The apparent accelerated spasticity should signal to the provider that a potential complication has arisen. Oral baclofen, dantrolene, and oral or parenteral benzodiazepines may be used to alleviate these symptoms. Complications occur in approximately 20% to 30% of all cases. Infectious complications occur more frequently in children, revised pumps, and those placed subcutaneously.31,32 Infection rate is 10%, with most infections presenting during the first month after placement.29 Most infections are caused by Staphylococcus species, with a recent increase in methicillin-resistant S. aureus.33 Serious infections and meningitis may arise even without local symptoms.33 The majority of infections require neurosurgical consultation and IV antibiotics. Direct concerns about baclofen pumps to the neurosurgeon.

IMPLANTABLE CENTRAL NERVOUS SYSTEM STIMULATORS

The pathogenesis of Parkinson's disease is thought to involve unregulated activity of the subthalamic nucleus and globus pallidus interna. High-frequency stimulation with implantable CNS devices is being used for suppression of parkinsonian and essential tremors. Neurostimulation is typically used if drug therapy has failed to control tremors. Neurostimulation is as efficient at controlling tremors as classic thalamotomy but is less invasive. Deep brain stimulation studies have shown a 40% to 75% improvement in motor scores as well as improvement of rigidity, bradykinesia, and postural instability.34 Reported complication rates range from 7% to 65%, with a decline in the number of reported complications as physician experience increases.34 Infection rates approach 3% to 10%.34 Patients may present to the ED with varied complaints, including problems related to the subcutaneous pulse generator, temporary or permanent paresthesias, dysarthria, disequilibrium, or failure of the neurostimulator to suppress tremors. Neurosurgical consultation is needed because these complaints may represent lead displacement or migration requiring surgical correction or replacement. If the diagnosis remains uncertain, observation with the stimulator in the off position may be required to help differentiate mechanical failure from an acute neurologic deficit.34

SPINAL CORD STIMULATION

Spinal cord stimulation is an established modality for treating chronic back pain, multiple sclerosis pain, complex regional pain syndromes, phantom pain, diabetic neuropathy, postherpetic neuralgia, angina pectoris, intractable pain associated with some malignancies, and the pain syndromes associated with vascular disease. Multicontact electrodes are placed in the epidural space, and the distal end of the electrode is connected to an internalized pulse generator. The therapeutic response is thought to be a result of stimulation of one of several dorsal tracts as well as activating the release of inhibitory neurotransmitters.35,36 Complications include dural puncture, spinal cord compression, CSF leak, hemorrhage, infection, abscess, epidural fibrosis, migration, interruption of wires, corrosion of contacts, and battery failure. The most frequent complication is device failure, accounting for 17% to 25% of complications.37 The rate of infection is reported between 2.5% and 5%.36 Patients with these devices should not undergo MRI.

PERIPHERAL NERVE STIMULATION

Peripheral nerve stimulators are used to treat neuropathic pain disorders in patients with chronic intractable pain such as with occipital neuralgia. The device is similar to other stimulators except that the electrodes are placed in the subcutaneous tissue overlying the peripheral nerves. Case reports of interference of stimulators causing pauses in cardiac pacemakers exist and thus must be considered in patients with both a pacemaker and stimulator and a new conduction abnormality.38

Acknowledgment: The author gratefully acknowledges the contributions of Dr. Joseph Pagane, the co-author of this chapter in previous editions.

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