Are there different types of Motor Neurone Disease?

The most common form of motor neuron disease is also referred to as Amyotrophic Lateral Sclerosis or ALS. This is considered the classical form of the disease. It typically presents with a combination of upper and lower motor neuron degeneration- which translates clinically in to a weak and/or stiff arm or leg- often beginning in one region (such as one arm or leg) and then progressing to involve other regions. Sometimes as the disease progresses there can be the development of cognitive problems- specifically the type of dementia referred to as frontotemporal dementia (see dementia page). These patients can also develop a high emotional lability as part of their syndrome. Often when this occurs the condition is referred to as ALS- plus syndrome.

There are other types or variants of motor neuron disease:

1. 1. Progressive Muscular Atrophy- this condition is diagnosed when only the lower motor neurons are involved. So a patient may notice a lot of muscle twitches or cramps and that the muscles are becoming weak and look thin or wasted (as in they have lost their usual bulk). This may progress to involve the upper motor neurons as well as time goes on or remain confined to the lower motor neurons.

1. 2. Primary Lateral Sclerosis- this condition is diagnosed when only the upper motor neurons are involved. In this case the patient may notice symptoms such as stiffness or spasms of muscles that may translate in to dragging the leg whilst walking or inability to manage to do up buttons because of dexterity issues. In general this condition is only formally diagnosed after about 3-4 years of having symptoms. This is because it is possible for ALS to present initially with only upper motor neuron involvement and then progress to the lower motor neurons. It is thought that after 3-4 years has elapsed that this type of progression is less likely.

1. 3. Progressive Bulbar Palsy- this condition is diagnosed when only the bulbar muscles (those responsible for speech and swallow function) are involved. The typical way that this condition presents is with difficulty with speech or swallowing or both. Again, there can be a combination of upper and lower motor neuron involvement here but ultimately for the patient the symptoms will be difficulty speaking and difficulty swallowing. Again this usually progresses to involve the arms and legs after a number of years.

1. 4. Flail Leg or Arm Syndrome- Here the predominant symptom is a lower motor neuron degeneration of one arm or one leg. It tends to begin in the muscles closer to the trunk and then spread down to involve the muscles in the hand or foot. This tends to remain in the one arm or leg. It can be very debilitating but is much slower in terms of progression than classic ALS.

1. 5. Kennedy Disease- This is an inherited condition. Some of the symptoms are similar to those of ALS and thus it may lead to diagnostic confusion. However there are some distinctive features. Kennedys disease is a slowly progressive condition involving degeneration of lower motor neurons that is caused by a genetic mutation. The diagnosis is usually made by means of the nerve conduction test- this will demonstrate that the nerves carrying sensory (and not just motor) function are also involved and this does not tend to happen in classical ALS. This condition does not affect life span.

There are also some conditions that may have some of the features that are similar to those found in motor neuron disease but are far more benign:

1. 1. Benign fasciculation syndrome- This is a condition that is characterised solely by muscle twitches. It may be the only reason you have sought an assessment with your GP or neurologist. A fasciculation is the medical term for a muscle twitch. The most frequent part of the body that they occur in are the calf muscles, hand muscles and eye-lids. They occur because the motor unit (group of nerve and muscle cells that work together to produce a muscle contraction) discharges spontaneously. It is thought to be due to nerve “hyperexcitability”. In some people drinking a lot of coffee can be a trigger. Exercise also appears to be a common trigger especially right after a workout during a rest period. When they are the only symptom that you are experiencing they are unlikely to be due to a sinister cause such as motor neuron disease. However, you will most likely have a test of your nerves (Nerve conduction studies and EMG- described on services page) in order to make sure that the nerves and muscles are otherwise functioning as normal. They are often associated with stress, anxiety and poor sleep so addressing these are likely to help reduce them. As a symptom they do not tend to be bothersome aside from being irritating. The main reason for consulting a neurologist is usually because the patient is worried about a more sinister cause. If, however, they are particularly bothersome there are some medications that may help by dampening down nerve hyperexcitability.

1. 2. Cramp fasciculation syndrome- This is another condition characterised by twitches in the muscles. Muscle cramping also occurs (this may be present in benign fasciculation syndrome but to a much lesser extent). The muscle cramps and twitches can be triggered by exercise. In general they cause more symptoms and more discomfort than the benign fasciculations (described above). Again, when you present to your neurologist with these symptoms you will most likely have a nerve conduction and EMG study to make sure the function of the nerves is otherwise normal. The underlying reason for the symptoms is thought to be nerve hyperexcitability and the symptoms can be treated with medications that dampen down nerve hyperexcitability.