PERIPHERAL NERVE DISORDERS
Acute Inflammatory Demyelinating Polyneuropathy (AIDP; Guillain-Barre Syndrome)
Acute inflammatory demyelinating polyneuropathy (AIDP) is a primarily demyelinating neuropathy with autoimmune etiology. Motor axons are affected more than sensory axons. Incidence in children is similar to that seen in adults. Children often have a prodromal respiratory or gastrointestinal infection occurring within 1 month of onset. Common precipitating infections include mycoplasma, cytomegalovirus, Epstein-Barr virus, Campylobacter jejuni, and various vaccinations. Weakness generally begins distally in the lower extremity with a progressive ascending paralysis ultimately involving the upper limbs. Pain and sensory symptoms are not uncommon. The most common cranial nerve abnormality is an ipsilateral or bilateral lower motor neuron facial paralysis. Objective sensory loss has been documented in the minority of children (154). In one series, only 15% required mechanical ventilation (155). The maximal degree of weakness generally reaches a peak within 2 weeks of onset and time to maximum recovery was 7 +/- 5 months in one series (156). Complete recovery occurs in most children. Classic criteria for poor recovery in adults (low median CMAPs and fibrillation potentials) may not apply to children (157).
Disturbances of the autonomic nervous system are common in children, including transient disturbances of bowel and bladder, excessive sweating or vasoconstriction, mild hypertension or hypotension, and occasionally cardiac arrhythmias.
The acute motor axonal neuropathy (AMAN) involves predominantly motor nerve fibers with a physiologic pattern suggesting axonal damage, whereas the AIDP involves both motor and sensory nerve fibers with a physiologic pattern suggesting demyelination. Another clinical variant is the Miller Fisher syndrome characterized by acute onset ataxia, ophthalmoparesis, and areflexia.
Diagnosis is generally confirmed by electrodiagnostic studies (see Chapter 6), and the CSF protein is characteristically elevated in a majority of children. Serum autoantibodies which may be elevated include IgM and IgG versus beta-Tubulin and heparin sulfate. AMAN patients may show increased IgG antibodies to GM1 ganglioside. The Miller Fisher syndrome is associated with a high frequency of the IgG GQlb antibodies. The major considerations in differential diagnosis of AIDP or AMAN include transverse myelitis, toxic neuropathies, tick paralysis, infantile botulism, myasthenia gravis, and dermatomyositis.
Treatment has typically included corticosteroids, plasma exchange, or more recently, intravenous immunoglobulin (IVIG; 158-161). AIDP patients respond to both plasma exchange and IVIG. Patients with AMAN respond preferentially to IVIG over plasma exchange. Recovery is often quite good in children without treatment. After standard IVIG therapy, children with axonal forms of Guillain-Barre syndrome recover more slowly than those with the demyelinating form, but outcome at 12 months appears to be equally favorable in two groups (162).
Chronic Inflammatory Demyelinating Polyradiculoneuropathy (CIDP)
Children with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) often have a presentation similar to AIDP; however, the disorder continues with a chronic or relapsing course. The disorder may begin as early as infancy, but is seen in children and adults. Electrophysiologic studies show focal conduction block, temporal dispersion of CMAPs, prolongation of distal motor latencies, markedly slow conduction velocities, and absent or prolonged H-wave and F-wave latencies. CIDP cases often demonstrate axonal loss on EMG. The CSF protein is elevated in most cases.
The differential diagnosis usually includes Charcot-Marie-Tooth (CMT) types I and III. The presence of acute relapsing episodes points toward CIDP. Due to the more severe involvement of proximal nerves and nerve roots, a distal sural nerve biopsy may not always show inflammatory changes and demyelination.
Treatment may include corticosteroids (prednisone) and IVIG as first-line approaches and subsequently plasma exchange.