Understanding ALS

Symptoms of ALS

We can tell that there is motor neuron damage by the symptoms that a person has and by our examination of the motor system (Figure 1 below). When the physician considers motor neuron disease (MND), he/she must evaluate whether there is damage to the motor system; where the damage is-i.e. whether the damage involves the UMN, the LMN, or both pathways; and whether there is any indication of damage outside the motor system (which could indicate a diagnosis of something other than MND). Sometimes we also need a special test called the EMG-NCV (Electromyogram and Nerve Conduction studies) to help us to detect damage to the lower motor neurons and to exclude more treatable diseases such as motor neuropathy with multifocal conduction block (See the section on classification of motor neuron diseases and the section on differential diagnosis).

Symptoms of damage to the UMN include stiffness, cramps, slowness of movement, laughing or crying too easily (termed pseudobulbar affect), nasal slow speech, and sometimes urgency of urination. The signs of upper motor neuron damage on exam include an increase in muscle tone or stiffness with resistance to movement called spasticity, increased reflexes (when the knee, ankle, inner elbow and arm are tapped with the reflex hammer), and abnormal reflexes (this includes an increase in chin movement with a tap called a jaw jerk, the presence of a Babinski sign where the big toe goes up instead of down when the sole of the foot is stimulated, and the presence of increased finger flexion on the appropriate stimulus).

Symptoms of LMN damage include weakness, thinning of the muscles or atrophy, twitching of the muscles or fasciculations, and cramps. The examination demonstrates weakness and atrophy with fasciculations and a decrease in tone with absent or diminished reflexes. The EMG will demonstrate damage due to LMN loss in the weakened muscles and may also show changes in muscles that are still strong. NCV should be normal. However, these studies are important because they help to detect motor neuropathy with or without conduction block in people with mainly LMN damage. Those individuals may have a motor neuropathy that is treatable.

It is very important to understand that the presence of motor neuron damage does not mean that someone has ALS or any other motor neuron disease. We must first rule out any other cause of the motor neuron damage. Below is a discussion of the differential diagnosis of ALS (i.e. the other things to consider).