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CHAPTER 34

Acute Flaccid Paralysis

Pathophysiology and clinical Further reading, 228 presentations, 226

Acute flaccid paralysis is defined as weakness in Anterior horn cell damage one or more limbs, or the respiratory or bulbar causing acute flaccid paralysis muscles, resulting from damaged lower motor Polio neurones. Poliomyelitis was the most important Infection with this enterovirus can be asympto- cause, but since it has declined other causes matic, can cause a mild non-specific febrile ill- have become more important. ness, viral meningitis or paralytic poliomyelitis, Classically, in acute flaccid paralysis there is which can be spinal or bulbar. Paralytic po- weakness with reduced tone (flaccid weakness) liomyelitis is biphasic, with a non-specific fever and reduced or absent reflexes. Differentiating followed by a brief afebrile period before the from upper motor neurone weakness is usually central nervous system (CNS) is invaded.This is straightforward, but it should be remembered heralded by further fever and an acute-onset that acute spinal shock (e.g. caused by trauma) asymmetrical flaccid paralysis of one or more can initially cause flaccid paralysis before spas- limbs, which may be painful. Since the World ticity develops. Health Organization campaign to eradicate polio using the oral polio vaccine, the number of cases has dropped from more than 350000 Pathophysiology and cases in 1988 to approximately 1900 cases in clinical presentations 2002. Most of these came from South Asia (India, Pakistan and Afghanistan), West Africa Broadly speaking, there are two pathophysio- (mainly Nigeria) and Central Africa (mainly De- logical processes that cause acute flaccid paraly- mocratic Republic of Congo). sis (Fig. 34.1). These are direct viral damage of lower motor neurone cell bodies in the anterior Enterovirus 71 horn of the spinal cord (e.g. polio, other en- Enterovirus 71 has caused epidemics of acute teroviruses, flaviviruses); and a para- or post- flaccid paralysis in recent years (especially in infectious immunologically mediated process Asia), often in association with hand, foot and damaging the motor nerves, and often sensory mouth disease. Many other enterovirus, Cox- nerves (e.g. Guillain–Barré syndrome), some- sackie virus and echovirus serotypes occasio- times caused by antibodies directed against the nally cause acute flaccid paralysis. gangliosides (glycolipids in the nerve cell mem- branes). Recognizing the clinical features of Japanese encephalitis virus these two patterns helps in determining the Japanese encephalitis virus,West Nile and other likely cause (Table 34.1). flaviviruses typically cause meningoencephalitis,

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Pathophysiology and clinical presentations 227

CAUSES OF ACUTE FLACCID PARALYSIS

Direct viral damage to anterior Immune-mediated damage to peripheral horn cells (e.g. polio) nerves (e.g. Guillain–Barré syndrome)

Paralysis onset During (or straight after) Several weeks after febrile illness febrile illness

Pattern of paralysis Asymmetrical Symmetrical

Time to reach Short (e.g. 2–3 days) Long (e.g. 7–14 days) maximum weakness

Sensory involvement No Often (depending on exact disease)

CSF Increased lymphocytes Increased protein (e.g. 100 mg/dL, (e.g. 100/mm3) especially late in the disease)

Pain Often limb muscle pain Often back pain

Table 34.1 Clinical features to distinguish causes but flaviviruses can also present with a pure flac- of acute flaccid paralysis. cid paralysis that can be clinically similar to polio (Chapter 33).

Immune-mediated causes of acute flaccid paralysis ACUTE FLACCID PARALYSIS Guillain–Barré syndrome is now recognized as a Immune-mediated damage (GBS) group of disorders classified according to the to myelin (AIDP) predominant type of nerve injury (axonal or de- to axons (AMAN) myelinating) and the main nerve fibres involved (motor, sensory, cranial). Different antiganglio- side antibodies are associated with different diseases.

Acute inflammatory demyelinating polyneuropathy (AIDP,or ‘classical’ Guillain–Barré syndrome) This typically presents several weeks after a Direct viral damage of anterior horn cells Polio, enteroviruses, echovirus, febrile illness with back pain, then symmetrical Coxsackie virus ascending flaccid paralysis and sensory changes. JEV, other flaviviruses Recovery is usual. Treat rapidly progressing symptoms with intravenous immunoglobulin if Fig. 34.1 Pathophysiology of acute flaccid available. paralysis. Immune-mediated Guillain–Barré syndrome (GBS) occurs in two forms: in acute Acute motor axonal neuropathy inflammatory demyelinating polyneuropathy (AMAN, or Chinese paralytic syndrome) (AIDP) the myelin is damaged; in acute motor This typically follows diarrhoea caused by axonal neuropathy (AMAN) the motor axons are Campylobacter jejuni. Symmetrical weakness is targeted.Viruses such as polio and Japanese encephalitis virus (JEV) cause paralysis by directly present with no sensory changes. Residual attacking the lower motor neurones (the anterior weakness is common. Occurs in summer epi- horn cells). demics in China. GBL34 11/27/03 3:49 PM Page 228

228 Chapter 34: Acute Flaccid Paralysis

Rare causes sensory nerves have reduced conduction veloc- Consider rare causes of paralysis if the diagnosis ities and delayed distal latencies because de- is not apparent. myelinated nerves conduct more slowly. •Any exposure to toxins? • AMAN (Chinese paralytic syndrome) — •Any tick bites (tick paralysis is a slowly motor amplitudes are reduced because motor ascending paralysis that recovers when the tick axons have been damaged. is removed)? • Exposure to rabid animal (paralytic rabies)? • History of a severe sore throat with neck swelling (diphtheritic neuropathy)? Further reading • Consumption of poorly preserved food (bot- ulinum toxin)? Anonymous. Progress toward global poliomyelitis eradication, 1999. Morbid Mortal Week Rep 2000; 49: 349–54. Nerve conduction studies Bolton CF.The changing concepts of Guillain–Barré Where available, nerve conduction studies may syndrome. New Engl J Med 1995; 333: 1415–16. help distinguish further: [Good explanation of acute motor axonal neu- • Anterior horn cell damage — motor amplitude is ropathy as a form of Guillain–Barré syndrome.] reduced because motor cell bodies have been Solomon T,Willison H. Infectious causes of acute flac- damaged. cid paralysis. Curr Opin Infect Dis 2003; 16: 375–9. • Classical Guillain–Barré syndrome (autoimmune [Annotated review of main infectious causes.] demyelinating polyneuropathy) — motor and