Motor Neurone Disease (MND) is a progressive neurological condition that directly affects the motor neurons—the nerve cells in the brain and spinal cord controlling voluntary muscles responsible for movement, speaking, swallowing, and breathing. The degeneration and death of these motor neurons interrupt the signals between the brain and the muscles, leading to muscle weakness and wasting. Amyotrophic Lateral Sclerosis (ALS), sometimes called Lou Gehrig’s disease, represents the most common form of MND in adults, involving both upper and lower motor neurons.
Identifying the Earliest Physical Changes
The first physical changes of MND are frequently subtle, making them easy to dismiss as normal fatigue, aging, or minor injury. One of the most common early signs is muscle fasciculations, which are involuntary, fine twitchings just beneath the skin’s surface, often described as a rippling sensation. These fasciculations are a sign of deteriorating lower motor neurons and can be observed in the arms, legs, or even the tongue.
People may also notice painful muscle cramping or a general feeling of stiffness known as spasticity, particularly in the limbs. This stiffness is related to damage to the upper motor neurons. Early muscle weakness is often asymmetric, meaning it begins in one limb rather than affecting both sides of the body equally. This localized weakness, along with muscle wasting, is what eventually prompts a person to seek medical attention.
Onset Patterns: Where Symptoms Begin
Motor Neurone Disease presents in one of two primary ways depending on where the motor neuron damage first appears. The majority of cases (approximately 70 to 75 percent) begin with “Limb Onset” MND, where initial symptoms manifest in the arms or legs. If the onset is in the legs, a person may experience foot drop, which is the inability to lift the front part of the foot, leading to tripping and a dragging gait. When the arms are affected first, subtle difficulties with fine motor skills become noticeable, such as struggling to button a shirt, turn a key, or write clearly.
The other main presentation is “Bulbar Onset” MND, which accounts for about 20 to 25 percent of cases. Bulbar onset involves the muscles controlled by the nerves in the brainstem (often referred to as the bulb). The first signs here involve difficulties with speech and swallowing. Speech may become slurred or nasal (dysarthria), and a person may experience difficulty chewing or swallowing food and liquids (dysphagia).
How Initial Symptoms Progress
Once the initial symptoms appear, Motor Neurone Disease is characterized by its progressive nature, meaning muscle weakness spreads and worsens over time. If the disease began in a limb, symptoms progress to the opposite limb, then the other two limbs, and eventually to the bulbar region. Conversely, in bulbar onset, the limb muscles eventually become involved as the disease advances.
The rate of progression varies significantly among individuals, but the spreading weakness eventually impacts critical functions. As the disease advances, the muscles used for breathing weaken, which can lead to respiratory insufficiency. Importantly, the disease spares certain neurological functions: a person’s senses (sight, hearing, and touch) remain intact. Cognitive function, memory, and control over bowel and bladder functions are also largely unaffected.
Seeking a Definitive Diagnosis
There is no single blood test or scan that can definitively diagnose Motor Neurone Disease; the process involves ruling out other conditions that mimic its symptoms. Diagnosis is managed by a specialist neurologist who relies on a detailed clinical history and physical examination. The neurologist looks for evidence of both upper and lower motor neuron damage in multiple body regions to confirm MND.
Specialized tests support the clinical findings and exclude other possibilities. Electromyography (EMG) and Nerve Conduction Studies (NCS) measure the electrical activity of muscles and nerves to detect patterns consistent with motor neuron damage. Magnetic Resonance Imaging (MRI) scans are performed not to diagnose MND, but to ensure symptoms are not caused by conditions like a spinal cord tumor or multiple sclerosis.