HOW PDN HAPPENS.
THE DAMAGE.

PDN IS A RARE CHRONIC DEMYELINATING NEUROPATHY found in association with a paraprotein, the presence of an excess amount of a single type of antibody in the blood. The 3 main types of antibodies or immunoglobulin (Ig) are IgM, IgG and IgA. Although IgG is the most common class amongst benign paraprotein bearers, the approximate proportions in PDN cases are IgM - 60%, IgG - 30% and IgA -10%. It may be reasoned that, in some manner, the excess protein/ antibody/immunoglobulin has recognised a protein associated with the myelin sheath as a foreign invader, and seeks to neutralize it. The protective coating or myelin sheath is damaged, rather like stripping the insulation off an electric wire, causing the nerve cells to not function properly. So PDN is regarded as an immune-mediated disorder. This demyelinating type of damage only happens very rarely amongst paraprotein bearing people. The damage is usually to the insulating myelin sheath coating of the nerve cells, but sometimes also to the axon . There are exclusively axonal varieties of this paraprotein-related neuropathy, mostly amongst some IgG bearers. The median age of onset of PDN is the 6th decade and there is a male predominance.

DEMYELINATION is the main damage from the inflammation that results from the presumed action of the paraprotein on the myelin. The central core of the nerve cells, the axons, is the cable and wires, which carry the nerve signals from the brain over the long distances of the peripheral nervous system. The insulating coat of the nerves, the myelin sheath normally speeds up the transmission of these signals. The damage of the partial stripping off of this protection has exposed the active nerve, the axon. The myelin damage and exposure of the axons, means that the signals cannot be transmitted efficiently. They are greatly slowed down. Varying levels of chaotic disorder in the behaviour of the motor nerves leading to the muscles for the feet and legs and/or the arms and hands stem from inappropriate messages being fired off in the damaged nerve chain. These include electric shocks, burning, pain, aches and intermittent feelings of tightness. Lack of nerve supply makes the muscle weak. Another symptom may be tiredness. The behaviour of the sensory nerves may also be considerably affected.

MIXED MOTOR AND SENSORY DAMAGE. PDN sufferers tend to have distal (damage at feet/legs, hands/arms), symmetric, mixed sensory - motor or predominantly sensory peripheral neuropathies that are slowly progressive. The severity of sensory loss in PDN's tends to be greater and the sensory nerve conduction more abnormal compared with CIDP. Foot numbness and paresthesias (abnormal sensations such as pins and needles, prickles, electric shock type feelings) can be common, but there is less severe motor weakness and functional impairment (muscular damage to feet/legs and hands/arms). Many PDN sufferers experience more pain than is the case for CIDP patients.

TO SUM UP, TYPICALLY PDN OR MGUS-associated neuropathy has these features:

1. The presence of paraprotein in the serum.

2. Various malignant disorders have been eliminated.

3. There is a symmetrical, sensorimotor polyneuropathy which has begun insidiously and has progressed slowly.

4. It has begun in the patient's 6th or 7th decade of life, but it may happen earlier.

5. Males are affected more than females.

6. Experiences such as numbness and tingling (parathesias), decrease in balance in some forms (ataxia) and pain may be quite prominent.

Please note: These notes are based on my experience and my reading of published professional material. They should not be understood as coming from any personal medical expertise. Should anyone, especially a professional neurologist, notice any error please contact me!