The diagnosis is made by genetic testing. Creatine phosphokinase (CK) may be normal or mildly elevated. The electromyelogram (EMG) shows fasciculations, fibrillations, and other signs of denervation. Muscle biopsy specimens show grouped atrophy.
No specific treatment delays progression of SMA, although a number of promising agents are being studied. Symptomatic therapy is directed toward minimizing contractures, preventing scoliosis, maximizing nutrition, and avoiding infections. Respiratory infections are managed early and aggressively with pulmonary hygiene, oxygen, and antibiotics. The use or nonuse of artificial ventilation and tube feedings must be individualized for each patient in each stage of the illness.
There are many peripheral nerve diseases in childhood, but the most classic presentations are: Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy (CIDP), hereditary motor sensory neuropathy (HMSN), and tick paralysis. Peripheral neuropathies produced by diabetes mellitus, alcoholism, chronic renal failure, exposure to toxins, vasculitis, and the effects of neoplasm are common in adults but are rare in children.
Guillain-Barré syndrome (acute inflammatory demyelinating polyradiculoneuropathy) is a postinfectious autoimmune peripheral neuropathy that can occur about 10 days after a respiratory or gastrointestinal infection (classically Mycoplasma pneumonia or Campylobacter jejuni). It occurs in people of all ages and is the most common cause of acute flaccid paralysis in children.
The characteristic symptoms are areflexia, flaccidity, and symmetrical ascending weakness. Progression can occur rapidly, in hours, or more indolently over weeks. Typically symptoms start with numbness or paresthesia in the hands and feet, then a heavy, weak feeling in the legs. Weakness ascends to involve the arms, trunk, and bulbar muscles (tongue, pharynx, larynx). Deep tendon reflexes are absent even when strength is relatively preserved. Objective signs of sensory loss are usually minor compared with the dramatic weakness. Bulbar and respiratory insufficiency may progress rapidly. Dysfunction of autonomic nerves can lead to blood pressure changes, tachycardia and other arrhythmias, urinary retention or incontinence, or stool retention. This polyneuropathy can be difficult to distinguish from an acute spinal cord syndrome. Preservation of bowel and bladder function, loss of arm reflexes, absence of a sensory level, and lack of spinal tenderness point toward Guillain-Barré syndrome. A cranial nerve variant of Guillain-Barré syndrome called the Miller Fisher variant manifests with ataxia, partial ophthalmoplegia, and areflexia.
The cerebrospinal fluid in Guillain-Barré syndrome is sometimes normal early in the illness but classically shows elevated protein levels without significant pleocytosis. Magnetic resonance imaging (MRI) with gadolinium may reveal enhancement of the spinal nerve roots. Electrophysiology studies (EMG, nerve conduction velocity [NCV]) are not always required but can provide corroborative diagnostic evidence and prognostic indicators.
Children in early stages of the disease should be admitted to the hospital. Those with moderate, severe, or rapidly progressive weakness should be cared for in an intensive care unit. Pulmonary and cardiac functions are monitored continuously. Endotracheal intubation should be performed in patients with impending respiratory failure or an inability to clear secretions. Most patients are treated initially with intravenous immunoglobulin (IVIG). Plasma exchange and immunosuppressive drugs are alternatives when IVIG treatment is unsuccessful or in rapidly progressive disease. Physical, occupational, and speech therapies are mainstays of treatment.