Multiple sclerosis (MS) is a chronic autoimmune disease where the immune system attacks the myelin sheath, the protective covering around nerve fibers in the central nervous system (brain and spinal cord). This demyelination disrupts the nervous system’s ability to transmit electrical signals efficiently. The resulting loss of signal integrity frequently manifests in the lower extremities, causing a wide range of sensory and motor issues in the legs and feet.
Sensory and Neuropathic Manifestations
MS often causes abnormal sensations in the feet due to misfiring or blocked nerve signals. These sensory changes are commonly described as tingling, prickling, or the sensation of “pins and needles.” A more painful form of altered sensation is dysesthesia, which can present as burning, aching, stabbing, or the feeling of an electrical shock. This neuropathic pain is a direct consequence of nerve damage in the central nervous system.
Numbness, or the loss of sensation, is another frequent symptom, sometimes described as feeling like the foot is encased in a thick glove. These sensory disturbances can be temporary or develop into chronic neuropathic pain that impacts daily life and sleep. Even when the feet feel intensely hot or cold, the skin itself may be a normal temperature, confirming the neurological origin of the sensation.
Motor Impairments and Mobility Issues
The disruption of nerve signals traveling from the brain to the muscles results in motor impairments in the lower legs and feet. Muscle weakness, specifically in the muscles responsible for lifting the front of the foot, is a common consequence. This weakness is often compounded by spasticity, an involuntary stiffness or tightening of the muscles, particularly in the calf, which makes movement difficult and painful.
Foot drop, the inability to properly lift the forefoot while walking, is a common motor symptom. This occurs because weakened muscles cannot adequately dorsiflex the ankle, causing the toes to drag or catch on the ground. To compensate, individuals often develop a “steppage gait,” lifting the knee high to clear the floor, which requires excessive effort and contributes to the fatigue common in people with MS.
Secondary Complications and Injury Risk
The combined effect of sensory loss and muscle weakness leads to secondary complications that increase the risk of injury. An altered gait, such as shuffling or dragging the foot, severely compromises stability and balance, increasing the risk of tripping and falling. Using more energy to walk also hastens the onset of fatigue, further impairing safe mobility.
The loss of tactile sensation, or numbness, creates a vulnerability to undetected injury. A person may not feel a cut, blister, or the pressure from an ill-fitting shoe, allowing minor injuries to worsen without notice. Altered weight distribution or immobility can also lead to skin breakdown and the formation of pressure sores where sensation is diminished. Regular foot inspection is necessary to check for issues the nervous system fails to register.
Strategies for Managing Foot Symptoms
Management of MS-related foot symptoms involves a combination of physical therapy, assistive devices, and medication aimed at addressing both motor and sensory issues. Physical therapy focuses on exercises that maintain joint range of motion, strengthen dorsiflexor muscles, and reduce spasticity through specific calf stretches. Neuromuscular reeducation techniques are also used to improve motor control by retraining nerve-muscle communication.
Assistive devices and pharmacological treatments are crucial for managing symptoms:
- Orthotic devices, such as an Ankle-Foot Orthosis (AFO), are common braces used to hold the foot in a neutral position and prevent toe drag.
- Functional electrical stimulation (FES) delivers small electrical impulses to the nerves, prompting the muscle to contract and lift the foot during the gait cycle.
- Pharmacological treatments, including medications targeting neuropathic pain or muscle relaxants, are utilized to reduce stiffness and improve comfort.