| BRAIN AND PERIPHERAL NERVE
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| Three weeks after an acute diarrheal illness, a 65-year-old man presented with progressive ascending weakness of the limbs followed by respiratory muscle weakness requiring assisted ventilation. On examination, he was hypotonic and areflexic, with profound general weakness. Isoelectric focusing of CSF and parallel serum samples showed a similar abnormal pattern of oligoclonal bands in both. |
| Comment. This predominantly motor neuropathy is Guillain- Barré syndrome and the patient has antibodies developed as a result of infection with the bacterium Campylobacter jejuni. The organism contains the antigen ganglioside sugar GM1, which is shared with a ganglioside on peripheral nerves. Antibodies bind to peripheral motor nerves and cause the neuropathy. It is an example of molecular mimicry. |
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| The distinction between brain and peripheral nerve essentially reflects the division between the central nervous system (CNS) and the peripheral nervous system (PNS): a convenient dividing line being the confines of the dura, within which watertight compartment is the CSF, partially produced (about one-third of the total volume) through the action of the blood-brain barrier. Myelin insulates the axons of nerves; the chemical composition of CNS myelin is quite distinct from that of PNS myelin, not least because the two forms are produced by two different types of cells: the oligodendrocyte within the CNS, and the Schwann cell within the PNS. The distinction between the separate functions of the CNS and
those of the PNS is fundamental to differential diagnosis in neurology, and many tests exist to discriminate between the two. A typical example is the difference between the demyelination of the CNS that occurs in multiple sclerosis, and the demyelination of the PNS that occurs in Guillain-Barré syndrome.
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