Poliomyelitis

This disorder is rare in developed countries, but should still be considered where there is acute onset of weakness of a single limb, or with patchy asymmetrical distribution, particularly if this is associated with fever, vomiting, neck or back stiffness, and muscle pain or spasms. Sensory abnormalities are absent.

Spinal muscular atrophy type I (Werdnig–Hoffmann disease)

This autosomal recessive disorder occurs in approximately 1 in 6000 live births, making it the most common fatal autosomal recessive disorder of early childhood. The earliest symptom may be decreased fetal movements in late pregnancy. Presentation is invariably before 6 months of age and is either at birth with hypotonia, weakness, joint deformity and respiratory difficulty, or more commonly later with marked hypotonia and limb weakness, poor feeding, poor cough and cry. The onset is sometimes relatively rapid and when first seen the child is usually severely weak (Fig. 17.3.1). Weakness, although generalized, is maximal proximally in the shoulder and hip girdle muscles. Intercostal muscle weakness leads to chest deformity, a poor cough and a weak cry. The respiratory pattern becomes diaphragmatic. Deep tendon reflexes are absent. Fasciculations of the tongue are an important clinical clue, but this can be a difficult sign to be certain about and one can only be confident if the baby is relaxed and there are no ‘voluntary’ movements of the tongue. Facial weakness in SMA is very mild and the extraocular movements remain full, giving the baby an alert appearance. Death, usually from pneumonia and respiratory failure, occurs by 18 months of age in 95% of patients, with those with onset in the first 2 months of life having the shortest survival.

Fig. 17.3.1 Child with spinal muscular atrophy type 1, showing profound hypotonia and weakness.

SMA is caused by homozygous deletions of the SMN1 gene, causing loss of SMN protein production in motor neurons of the anterior horn of the spinal cord. Prenatal diagnosis and carrier testing of relatives are available.

Various therapeutic strategies are being trialled. Most are designed to upregulate SMN protein expression via a variety of mechanisms.

Spinal muscular atrophy type 2

The genetic abnormality in SMA types 2 and 3 is allelic to that of SMA type 1, but these are milder forms of the disease. The clinical onset of SMA type 2 is almost invariably before 3 years of age, with hypotonia, weakness and delayed motor milestones. The clinical picture is one of severe generalized weakness and wasting, with proximal predominance. Deep tendon reflexes are decreased or absent and often there are fasciculations of the tongue. The facial muscles may be mildly weak but eye movements remain normal and the patient is usually normal intellectually. Many patients have a fine, rapid tremor of the hands. Children with SMA type 2 never walk unsupported. Survival varies from 18 months through to adult life. Major management problems include the prevention of orthopaedic deformity, especially scoliosis, and the management of the respiratory complications of muscle weakness. Prompt treatment of chest infections prolongs survival, and many children and adults with SMA type 2 benefit from nocturnal non-invasive ventilatory support. Patients with a later onset and a moderately benign clinical course are classified as SMA type 3 (Kugelberg–Welander syndrome). Most have onset in the first two decades, with only a few in the third decade, and survival is usually for many decades. Persons with SMA type 3 are able to walk at some point, and many remain ambulant into adulthood.

Guillain–Barré syndrome

GBS is the most common acute neuropathy in clinical practice and can occur at any age, although it is rare in infancy. An infection, commonly of the upper respiratory tract or gastrointestinal tract (Campylobacter jejuni), precedes the neurological syndrome in at least 50% of cases. Typical GBS is a monophasic illness with symmetrical, ascending weakness involving proximal and distal muscles. Paraesthesia and muscle pain may be presenting complaints but sensory impairment is usually minimal. Severe back pain and stiffness may occur, especially in young children. The deep tendon reflexes are lost early in the course of the illness. Cranial nerve involvement, particularly of the facial nerve, is relatively common. Autonomic involvement can cause wide fluctuations of the blood pressure as well as cardiac arrhythmias and bladder dysfunction. Respiratory failure occurs in about 30% of patients. GBS typically progresses over less than 4 weeks, with most patients reaching their maximal deficit within 2 weeks of onset. Artificial ventilation is occasionally required. Recovery continues over weeks to months, with most children returning to normal function. Some more severely affected children have residual weakness, most commonly of ankle dorsiflexion. Fatigue is common during the recovery period.

Diagnosis is based on the clinical features, with increased cerebrospinal fluid (CSF) protein with only a few, if any, cells in the CSF. Spinal magnetic resonance imaging (MRI) and/or nerve conduction studies are useful in difficult diagnostic situations. All children with suspected GBS should be admitted to hospital for monitoring of their respiratory status, blood pressure and cardiac rhythm. Management of GBS requires special expertise in medical and nursing care, and affected children should be referred to centres used to dealing with this condition. Supportive therapy is very important. Intravenous gammaglobulin or plasmapheresis, if used early, may hasten recovery, but is not always required for milder cases.

Chronic inflammatory demyelinating peripheral neuropathy (CIDP)

This rare but treatable autoimmune neuropathy presents subacutely or as a chronic neuropathy. The course can be monophasic but is more commonly relapsing/remitting. Acute presentations can occur and may cause confusion with GBS. Symptoms and signs of weakness, often most prominent proximally, bring the child to medical attention. The diagnosis is confirmed by nerve conduction studies, increased CSF protein and, if there is diagnostic doubt, pathological abnormalities on nerve biopsy. CIDP is treated with intravenous immunoglobulin, corticosteroids and other immunosuppressive agents.