MMN - What are the symptoms of Multifocal Motor Neuropathy?

Last week we took a look into MMN as a whole - what is this rare condition? What does diagnosis and treatment look like? And of course, what are the symptoms of MMN? This week, we're diving into that last question in a little more detail. We'll look at some of the early signs, and key symptoms you should look out for.

 Early Signs of MMN

MMN often starts subtly, which makes it easy to miss in the early stages. Many people later diagnosed with the condition noticed a weakness in one hand or arm at first.

Someone with that weakness may struggle to grip certain objects like cutlery, have difficulty buttoning a shirt, or feel a little clumsier than usual - they may accidentally drop a pen, or drop a mug instead of gripping the handle.

MMN is also slow and progressive. Unlike some other Inflammatory Neuropathies where symptoms can seemingly strike overnight - MMN's impact can build for months or even years before a diagnosis.

MMN is asymmetrical. That means it impacts one side more than the other. In MMN, you should not feel that your arms or legs are equally as weak or impacted.

 Symptoms

MMN impacts the motor nerves, so someone with the condition may experience:

Asymmetrical progressive muscle weakness in your limbs

Impacting one side more than the other, your arms and legs gradually get weaker and, in some cases, stiffer.

Muscle atrophy may occur in impacted areas

The muscles 'waste' away, or grow smaller/less toned/less powerful.

You may experience muscle twitches

You may hear or read this described as 'fasciculations', these twitches/spasms shouldn't cause pain like a cramp but can be annoying if you're trying to rest or sleep.

Foot drop

Difficulty lifting the foot when walking resulting in the foot striking the ground between strides - you may notice this at first as your foot dragging or catching the ground more often as you walk. Some people have told us this is like wearing new shoes with a much thicker sole. This can cause trips or falls.

Fatigue related to muscle weakness

Your muscles may be tired, but you yourself may also feel more tired as you compensate for the weakness by working harder. The fasciculations can also make sleep harder, resulting in fatigue.

 MMN shouldn't..

Cause sensory symptoms like tingling or pain. There may be some pain, discomfort, or numbness due to associated muscle issues - but it should not be a direct symptom.

 How is MMN different from GBS or CIDP?

While GBS and CIDP can share a lot of early symptoms and therefore see some cross/misdiagnosis - MMN differs in many ways from GBS and CIDP. Two of the most obvious differences are:

It impacts the motor nerves, not the sensory nerves

So the 'trademark' pins-and-needles feeling of GBS/CIDP is absent

It's asymmetrical

Whereas in GBS/CIDP, the impact tends to be more symmetrical

 What should you do if you think you may have MMN?

If you're experiencing unexplained muscle weakness, particularly if it's slowly progressing/getting worse - it's important to talk to your GP who can refer you to a neurologist for tests (more on this to follow).

Whether it is MMN or not, it's important to find out what is causing this impact to your muscles. In the case of MMN, the sooner you can get on the right treatment, the less you'll feel its impact. And if you are diagnosed with MMN, we're here to support you.

 Support for MMN

Living with Multifocal Motor Neuropathy can be challenging, but you don’t have to face it alone. Inflammatory Neuropathies UK is here to support people and families affected by MMN. We provide trusted information, advice, and guidance; practical support where it’s needed; fund and undertake research; and raise awareness of rare Inflammatory Neuropathies. If you’d like to know more, you can read our blog series, explore our resources, or get in touch.

If you’re looking for support, to have a chat or ask questions, why not join our Facebook Group or read our Newsletter.