Clinical manifestations of UMNS are commonly classified into positive and negative signs. Positive signs include hyperreflexia, spasticity, involuntary muscle spasms, and clonus. Negative signs include reduced dexterity, muscle weakness, and impaired muscle control. Over time, secondary changes such as joint contractures and muscle shortening may occur over time.
Spasticity is a possible symptom of UMNS, although the terms are used interchangeably. Management addresses functional limitations, abnormal muscle activity, and secondary complications associated with the underlying neurological condition that is precipitating UMNS.
Signs and symptoms
The location and extent of the neurological lesion determine how UMNS manifests clinically. Manifestations include positive and negative signs, which could lead to secondary changes affecting muscles and connective tissues.
Positive signs
Positive signs are defined as increased or involuntary muscle activity and exaggerated stretch reflexes. The widely accepted definition of spasticity is a velocity-dependent increase in muscle tone or resistance to passive muscle stretch, which is associated with abnormal stretch reflexes. Another sign is clonus, which consists of repetitive, involuntary muscle contractions that are elicited by sustained muscle stretch, usually seen at the ankle. Hyperreflexia is characterized by exaggerated deep tendon reflexes (DTR), and involuntary muscle spasms or irregular muscle activation may occur.
Negative signs
Negative signs are characterized by reduced voluntary motor function, including muscle weakness, impaired dexterity, and reduced selective motor control ability. These manifestations may make coordinated movements such as reaching, grasping, walking, or sitting up more difficult. This can lead to issues involving activities of daily living, mobility, and posture.
Category
Clinical Manifestation
Description
Positive Signs
Spasticity
Velocity-dependent increase in tone/resistance to passive muscle stretch/movement
Hyperreflexia
Exaggerated deep tendon reflexes
Clonus
Repetitive, involuntary muscle contractions
Muscle Spasms
Uncontrolled muscle contractions
Negative Signs
Muscle Weakness
Reduced voluntary force generation by muscles
Impaired Dexterity
Difficulty executing precise movements
Reduced Selective
Motor Control
Difficulty activating muscles/muscle groups independently
Secondary Musculoskeletal Changes
Muscle Shortening
Reduced muscle length
Joint Contracture
Persistent restriction of joint range of motion due to changes in soft tissue
Increased Passive
Stiffness
Resistance to movement due to tissue changes
Causes
Upper motor neuron syndrome is seen in conditions where descending motor pathways within the brain or spinal cord are injured. These include spinal cord injury, cerebral palsy, multiple sclerosis and acquired brain injury including stroke. These conditions may affect different neural pathways involved in movement, posture, and spinal reflexes.
Pathophysiology
Development of UMNS is brought on by the disruption of descending pathways that control spinal motor units. Normally, excitatory and inhibitory signals are sent along these pathways to influence spinal motor neurons and interneurons. When these pathways are damaged, voluntary muscle recruitment is altered due to impaired activity of spinal reflex circuits. This reduced motor unit recruitment can lead to impaired coordination and contributes to possible weakness.
Schematic representation of corticospinal pathway and the connections with spinal interneurons, lower motor neurons, and skeletal muscle.
Spinal reflex pathways are commonly altered due to changes in the descending input from the spinal cord. The lack of a consistent relationship between inhibitory and excitatory signals in the spinal neural network contribute to excessive muscle responses to movement or stretches. For example, if the pathways sending inhibitory signals is damaged, the muscle fibers will continuously receive excitatory input, causing unopposed muscle contraction.
Following acute spinal cord injury, a phenomenon coined spinal shock may occur, which presents with reduced muscle town and diminished or absent deep tendon reflexes below the level of the injury. As time passes, spinal reflex activity returns, leading to hyperactive reflexes and possibly spasticity.
After injury, reduced movement and immobilization of a muscle in the shorted position can lead to fibrotic changes in muscle fibers and connective tissue after a prolonged period of time. These changes increase resistance to passive stretching independent of irregular reflexes. Stiffness of muscles encounter during examination can thus be explained by neural and non-neural mechanisms.
Diagnosis
Assessment of motor control may involve several health professionals depending on the affected individual's situation, and the severity of their condition. This may include physical therapists, physicians (including neurologists and physiatrists) and rehabilitation physicians, orthotists, occupational therapists, and speech-language pathologists. Assessment is needed of the affected individual's goals, their function, and any symptoms that may be related to the movement disorder, such as pain. A thorough assessment then uses a clinical reasoning approach to determine why difficulties are occurring. Elements of assessment will include analysis of posture, active movement, muscle strength, movement control and coordination, and endurance, as well as muscle tone and spasticity. Impaired muscles typically demonstrate a loss of selective movement, including a loss of eccentric control (decreased ability to actively lengthen); this decreased active lengthening of a muscle is a key factor that limits motor control. While multiple muscles in a limb are usually affected in the Upper Motor Neuron Syndrome, there is usually an imbalance of muscle activity (muscle tone), such that there is a stronger pull on one side of a joint, such as into elbow flexion. Decreasing the degree of this imbalance is a common focus of muscle strengthening programs. Impaired motor control also typically features a loss of stabilisation of an affected limb or the head from the trunk, so a thorough assessment requires this to be analysed as well, and exercise to improve proximal stability may be indicated.
Secondary effects are likely to impact on assessment of impaired muscles. If muscle tone is assessed with passive muscle lengthening, increased muscle stiffness may affect the feeling of resistance to passive stretch, in addition to neurological resistance to stretch. Other secondary changes such as loss of muscle fibres following acquired muscle weakness are likely to compound the weakness arising from the upper motor neuron lesion. In severely affected muscles, there may be marked secondary changes, such as muscle contracture, particularly if management has been delayed or absent.
Treatment
Treatment should be based on assessment by the relevant health professionals. For muscles with mild-to-moderate impairment, exercise should be the mainstay of management, and is likely to need to be prescribed by a physical therapist or other health professional skilled in neurological rehabilitation.
Muscles with severe impairment are likely to be more limited in their ability to exercise, and may require help to do this. They may require additional interventions, to manage the greater neurological impairment and also greater secondary complications. These interventions may include serial casting, flexibility exercise such as sustained positioning programs, and medical interventions.
Research has clearly shown that exercise is beneficial for impaired muscles, even though it was previously believed that strength exercise would increase muscle tone and impair muscle performance further. Also, in previous decades there has been a strong focus on other interventions for impaired muscles, particularly stretching and splinting, but the evidence does not support these as effective. One of the challenges for health professionals working with UMNS movement disorders is that the degree of muscle weakness makes developing an exercise programme difficult. For muscles that lack any volitional control, such as after complete spinal cord injury, exercise may be assisted, and may require equipment, such as using a standing frame to sustain a standing position. Often, muscles require specific stimulation to achieve small amounts of activity, which is most often achieved by weight-bearing (e.g. positioning and supporting a limb such that it supports body weight) or by stimulation to the muscle belly (such as electrical stimulation or vibration).
Medical interventions may include such medications as baclofen, diazepam, dantrolene, or clonazepam. Phenol injections or botulinum toxin injections into a muscle belly of the upper or lower extremities can be used to attempt to dampen the signals between nerve and muscle. The effectiveness of medications varies between individuals, and varies based on location of the upper motor neuron lesion (in the brain or the spinal cord). Medications are commonly used for movement disorders, but research has not shown functional benefit for some drugs. Some studies have shown that medications have been effective in decreasing spasticity, but that this has not been accompanied by functional benefits.
↑Ada L, Dorsch S, Canning C G. Strengthening interventions increase strength and improve activity after stroke: a systematic review. Australian Journal of Physiotherapy. 2006;52(4):241–248.
↑Bovend'Eerdt TJ, Newman M, Barker K, Dawes H, Minelli C, Wade DT. The effects of stretching in spasticity: a systematic review. Arch Phys Med Rehabil. 2008 Jul;89(7):1395-406.
12Taricco M, Adone R, Pagliacci C, Telaro E. Pharmacological interventions for spasticity following spinal cord injury. Cochrane Database of Systematic Reviews 2000, Issue 2. Art. No.: CD001131.
↑Shakespeare D, Boggild M, Young CA. Anti-spasticity agents for multiple sclerosis. Cochrane Database of Systematic Reviews 2003, Issue 4. Art. No.: CD001332.
