WORDS RACHEL SOON

“I couldn’t feel the burn!!!” Peripheral neuropathy’s silent decay 

What happens when our sense of touch misfires? What happens when your fingertips feel the pricking of invisible needles, or can’t feel the heat from an open flame? This month, HealthToday consults physician and neurologist Dr Hiew Fu Liong on the stealthy onset of peripheral neuropathy and why it often goes unnoticed, especially among diabetics and the elderly.

A tired man settles into his favourite chair at home, rubbing his feet. These days they always get numb towards the evening. Poor circulation, he thinks, but that’s just part of getting older. On the table is a basin of steaming water prepared by his wife, and he gratefully puts it on the floor and sticks his feet in to soak. He lies back in his chair, eyes closed and relaxing.

Ten minutes later,  his wife comes in and gasps, staring at his feet. Horrified, she exclaims: “That water was just boiled! It hasn’t cooled yet!” The man finds himself rushed to the hospital with second- and third-degree burns. He can see the skin peeling from his feet, but he feels nothing at all.

WHAT IS PERIPHERAL NEUROPATHY?

Peripheral neuropathy is a condition where our nerve cells are damaged in a way that interrupts or changes the messages being sent between our brain and spinal cord (known as the central nervous system, or CNS) and the rest of our body.

We can think of our body as having a phone network. Whenever we interact with the world around us with any part of our body—through sight, sound, touch, smell, or taste— electrical signals are sparked and sent through a network of fibres, called nerves, to the CNS, which helps read those signals and send new ones back. This network goes all the way to the outermost (peripheral) parts of our body and is known as the peripheral nervous system (PNS).

How do our nerves carry these electrical signals? Like phone or power cables, nerves are long and thin cells, which consist of layers of protective insulation (a myelin sheath), wrapped around a delicate electrical conductor (an axon).

If both the myelin sheath and the axon are intact, signals can travel between the CNS and the PNS as they’re meant to be. However, if either the sheath or axon are damaged, these signals may be incomplete, changed, or even fail to reach the CNS.

This disrupted signalling can cause us to feel sensations that have no physical cause. Alternately, it can also cause us to feel no sensations even when something should be triggering them. It can also cause problems with movement if the parts of the PNS leading into our muscles can’t receive signals from the CNS, which tell them how to move.

Consider two persons having a phone conversation. If the line is good, they can hear every word the other person says. However, if the line is damaged somewhere along the way, they might miss parts of the conversation, or be disconnected halfway through.

WHAT ARE THE SIGNS OF PERIPHERAL NEUROPATHY?

The trouble with peripheral neuropathy is how different the symptoms (see inset box) can be from one person to another, as well as how gradually the symptoms develop. It can go unrecognized or uninvestigated for years because early signs are usually dismissed as a natural part of ageing or other conditions.

Symptoms to look out for:

• Tingling, burning, shooting, stabbing, and/or “electric shock”-like sensations
• Numbness
• Extreme sensitivity to touch
• Tachycardia (accelerated heartbeat even when resting)
• Muscle weakness
• Dizziness
• Sweating
• Acute discomfort in the extremities (hands, feet).

Peripheral neuropathy can lack symptoms entirely during its early stages. It’s estimated that up to 50% of people with diabetes and peripheral neuropathy don’t have symptoms.

At a later stage, it can result in numbness so severe that sufferers fail to notice injuries on their limbs, especially their feet. On the other hand, some experience hypersensitivity to a degree where they are unable to feel a breeze without feeling pain.’

The most commonly affected areas are the hands and feet, but other areas of the body can also be affected.

WHAT CAUSES PERIPHERAL NEUROPATHY? WHO’S AT RISK?

More than 20% of people with peripheral neuropathy develop the condition for no apparent reason. The rest can be due to one or more of the following sources of nerve damage:

• Complications from another disease. Globally, diabetes is the most common cause of peripheral neuropathy; it’s responsible for an estimated 35% of all cases. Cancer, infections and inflammatory diseases are also known causes.
• Ageing, with an estimated 8.1% of people aged 40 to 49 years, and 34.7% of those aged above 80 years affected.
• Exposure to environmental toxins, such as cigarette smoke and excessive alcohol.
• Nutritional deficiency. A lack of essential nutrients, especially vitamins B1, B6 and B12, is known to impair nerve recovery.
• Genetic conditions, such as mutations inherited from one’s parents or a spontaneous mutation occurring during one’s lifetime.
• Side effects from certain medications, which may directly or indirectly affect the nerves.
• Repetitive or prolonged nerve pressure from activities such as typing, cooking, or prolonged sitting. Carpal tunnel syndrome is a form of peripheral neuropathy.
• Physical injury such as trauma from motor accidents, falls, or sports.

As a result, groups of people at higher risk of developing peripheral neuropathy include the elderly (over 60 years), those with diabetes, smokers, heavy drinkers, vegetarians and others on exclusionary diets, the malnourished, patients with renal impairment, and those with impaired gastrointestinal functions due to disease, medication, or recent surgeries.

WHAT CAN BE DONE ABOUT IT?

Early diagnosis is crucial. If treatment starts early enough, many cases of peripheral neuropathy can be prevented, reversed or at least controlled before nerve damage reaches a point of no return. A doctor can examine a patient by testing what sensations they feel from gentle pressure by small tools, such as tuning forks, cotton, pin, and/or a biothesiometer.

Physicians may use validated questionnaires (eg, DN4 or painDETECT), which provide a set of questions that can be scored to see if a patient might need follow- up with a specialist. The specialist can do a nerve conduction study to directly check for signs of nerve damage.

Treatment focuses on regenerating the nerves, addressing the reasons behind the ongoing nerve damage, as well as alleviating symptoms.

B vitamins at medical-grade doses (higher than those in food supplements) may help damaged nerves regenerate, particularly in patients with nutritional deficiencies due to age, lifestyle, and/or certain medications.

Some patients may need antidepressants or anticonvulsants to control neuropathic pain. Physiotherapy and rehabilitation can help restore muscle and nerve function. Adjustments to existing medications and lifestyle behaviours may also be required, but only after the risks and benefits have been assessed by a doctor.

There’s evidence that acupuncture can help relieve symptoms, but look out for a certified acupuncturist, as needles can cause further nerve damage or infection, if not properly handled.

To date, there is no single effective treatment for peripheral neuropathy, but a  combination of pharmacological and non- pharmacological treatments can collectively contribute to easing symptoms and stopping—or even curing—the disease, as long as the signs are caught in time. HT

HOME RELIEF

If you or someone in your home has confirmed peripheral neuropathy, here are some recommended steps to take at home to relieve symptoms. However, these measures should only complement, but not replace, treatment by a trained medical professional.

• Always check hands and feet for any injuries or ulcers, especially if diabetes is also involved.
• Keep warm as symptoms usually worsen at night or with cooler temperatures.
• Wear gloves to sleep or reduce air-conditioning use.
• Gloves and long sleeves also help protect the skin for those who are touch sensitive.
• Keep affected areas out of the direct path of air-conditioning eg, while driving.
• Certain ointments such as capsaicin gels can provide pain relief when rubbed into affected areas.

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