Upper motor neuron syndrome is what you see after a stroke, a brain or spinal cord injury, or any other lesion of the descending motor pathways. Some signs appear that should not be there, such as spasticity, clonus and spasms. Other abilities disappear, such as strength and fine control of the hand. Spasticity usually gets most of the attention. However, the signs that disappear explain most of the disability.
This guide sorts the positive and negative signs of upper motor neuron syndrome by what drives them. It also shows how they combine into the typical postures you see in the clinic, and what this means for rehabilitation.
What is upper motor neuron syndrome?
Upper motor neuron syndrome is a collective term for the motor behaviors that follow a lesion of the descending corticospinal system [1]. The lesion can sit in the cortex, the internal capsule, the brainstem or the spinal cord. The cause matters less than you might expect. In fact, the clinical picture depends more on the location and extent of the lesion, and on the time since it occurred, than on its pathology [2].
The clinical features have traditionally been divided into two groups [1]. Positive features are overt behaviors produced by muscle overactivity. Negative features, in contrast, are behaviors that are lost, because the patient can no longer activate and control muscles normally. Both groups limit mobility and the use of the limbs [1].
| Positive signs | Negative signs |
|---|---|
| Spasticity | Muscle weakness |
| Increased tendon reflexes | Loss of dexterity |
| Clonus | Fatigability |
| Flexor and extensor spasms | |
| Babinski sign | |
| Spastic co-contraction | |
| Associated reactions | |
| Spastic dystonia |
The table follows Thibaut and colleagues [3], while Trompetto and colleagues also list the positive support reaction among the positive signs [4].
Negative signs come first
The two groups do not appear at the same time. After a stroke or trauma, weakness and loss of dexterity are apparent immediately [4]. Early on, the muscles may also be hypotonic, with reduced tendon reflexes. The positive signs appear later. The Babinski sign is the only one that tends to show up soon after the lesion [4]. Sheean points out that this delayed onset suggests plastic changes in the nervous system, not simply an imbalance of descending control [2].
Negative signs: what the patient loses
Weakness
Weakness is the central negative sign of upper motor neuron syndrome. The muscles produce less force because they lose their corticospinal drive [3]. In other words, the brain can no longer recruit enough motor units. Thibaut and colleagues describe a loss of functional motor units and a marked drop in the firing rate of the units that remain [3]. As a result, muscle contraction becomes less efficient, and every movement costs more effort.
Gracies defines paresis in the same way: reduced voluntary recruitment of motor units [5]. He also warns that it gets worse with time if the limb is not used. Chronic disuse changes the higher centers and further reduces the ability to recruit motor units. Gracies calls this the vicious cycle of paresis, disuse and paresis.
Loss of dexterity
After an upper motor neuron lesion, the patient loses precise hand movements. For example, opposition of the thumb becomes difficult, because the intrinsic and extrinsic hand muscles are weak [3]. Li and Francisco note that isolated lesions of the corticospinal tract in animals produce weakness, loss of dexterity, hypotonia and reduced reflexes, but not spasticity [6].
Fatigability
Because each movement needs more effort, patients tire quickly [3]. However, fatigability is easy to miss in a short assessment. Therefore, watch how performance changes over repeated tasks, not only at the start of the session.
Why the negative signs matter most
It is tempting to blame tone for poor movement. Yet O’Dwyer and colleagues found no relationship between spasticity and either weakness or loss of dexterity in 24 patients after stroke [7]. In fact, none of the positive and negative features they measured were correlated. Dromerick reaches a similar conclusion: slowness and incoordination come from incomplete and disordered activation of motor units, not from the passive resistance of spasticity [8].
Positive signs: what appears
The positive signs of upper motor neuron syndrome are all forms of muscle overactivity. However, they do not share one mechanism. Trompetto and colleagues sort them into two families [4]. Some come from hyperexcitable spinal reflexes. Others are efferent, which means they come from abnormal descending drive rather than from reflexes.
Signs driven by spinal reflexes
A hyperexcitable stretch reflex produces spasticity, clonus and increased tendon reflexes [4]. Spasticity in the strict sense depends on the speed of the stretch. We cover this in Lower Limb Spasticity: 5 Things Physiotherapists Should Know. Pandyan and colleagues proposed a broader definition: “disordered sensori-motor control, resulting from an upper motor neurone lesion, presenting as intermittent or sustained involuntary activation of muscles” [9].
Clonus is a series of involuntary, rhythmic contractions and relaxations of a stretched muscle [3]. We explain how to test it in Ankle Clonus: Causes, Testing and What It Means.
Other reflexes are also affected. An overexcitable flexor withdrawal reflex produces flexor spasms of the lower limbs, which are common after spinal cord injury [4]. Spasms can occur spontaneously or after a stimulus such as moving the leg or changing position, and the most common flexor spasm bends the hip, knee and ankle [3]. Finally, the release of primitive reflexes produces the Babinski sign and the positive support reaction [4]. In the Babinski sign, the big toe extends and the other toes fan out when you stroke the sole, which indicates a lesion of the corticospinal tract [3].
Efferent signs: overactivity during movement and at rest
Spastic co-contraction. Normally, a voluntary command activates the agonist and inhibits its antagonist through reciprocal inhibition. After an upper motor neuron lesion, this inhibition fails, so agonist and antagonist contract together, for example the wrist flexors and extensors [4]. Trompetto and colleagues consider co-contraction probably the most disabling form of muscle overactivity, because it hampers both force and movement.
Associated reactions. These are involuntary movements of paretic muscles. They appear when the patient uses unaffected muscles, or during events such as yawning, sneezing and coughing [4]. For example, the elbow often flexes and the arm lifts while a hemiplegic patient walks.
Spastic dystonia. This is a tonic contraction of a muscle at rest, best described as a relative inability to relax [4]. It is not caused by stretch, but it is sensitive to stretch and muscle length. A stretch can trigger it, while a prolonged stretch can reduce it. Spastic dystonia also shapes the resting posture: a flexed, adducted arm and an extended leg [4].
Indeed, spastic dystonia may be more common than many clinicians think. Trompetto and colleagues recorded the wrist flexors of 23 people with increased wrist flexor tone after stroke [10]. Spontaneous, stretch-sensitive muscle activity was present in 17 of them. The authors concluded that only a minority of these patients had spasticity.
Clinical tip
Before you test tone, look at the relaxed limb and ask the patient to let go. Activity that is present at rest points to spastic dystonia. Resistance that appears only with a fast stretch points to spasticity. Opposing muscles that switch on together during a voluntary movement point to co-contraction. Each one therefore needs a different plan.
How the signs shape posture
In upper motor neuron syndrome, the positive and negative signs rarely hit opposing muscles equally. Gracies notes that paresis, contracture and spastic overactivity are each distributed unevenly between agonists and antagonists [11]. This imbalance of torque around a joint produces the typical limb deformities. After stroke, the arm usually flexes and the leg usually extends [6].
The table shows common upper limb postures, the muscles most often involved and the problems they cause. It is based on Thibaut and colleagues [3], with the elbow flexors taken from Kovalenko and colleagues [12]. For the leg, see Lower Limb Spasticity: 5 Things Physiotherapists Should Know.
| Posture | Muscles often involved | Typical problems |
|---|---|---|
| Shoulder adduction and internal rotation | Pectoralis major, teres major, latissimus dorsi, anterior deltoid, subscapularis | Shoulder pain and stiffness, difficulty dressing and reaching forward |
| Elbow flexion | Brachioradialis, brachialis, biceps brachii | Elbow stays flexed in sitting, standing and walking; harder transfers and dressing |
| Forearm pronation | Pronator teres, pronator quadratus | Difficulty reaching underhand and holding a spoon |
| Wrist flexion | Flexor carpi radialis, flexor carpi ulnaris, palmaris longus | Median nerve compression at the wrist, weaker grip |
| Clenched fist | Flexor digitorum superficialis and profundus | Nails dig into the palm, skin maceration and breakdown |
| Thumb in palm | Flexor pollicis longus and brevis, adductor pollicis, first dorsal interosseous | The web space cannot open for grasp |
A posture is a map, not a diagnosis
However, a typical posture does not tell you which muscle is overactive. Kovalenko and colleagues tested 27 muscles one by one in 129 patients with chronic spasticity after stroke [12]. Spasticity was found in over 70% of cases for pectoralis major, brachioradialis, pronator teres, flexor carpi radialis, the long finger flexors and flexor pollicis longus. By contrast, it was found in only 35.8% for biceps brachii. In the leg, the medial gastrocnemius was involved in 48% of patients and the soleus in 19.6%. Surprisingly, the hip adductors showed no spasticity at all in this group. So use the posture as a map, and then test each muscle.
What upper motor neuron syndrome means for rehabilitation
Current treatments for spasticity act mainly on the positive signs [8]. They can ease painful spasms and resistance to passive movement. Still, reducing tone does not reliably restore function, because the main limitation is weak and poorly controlled activation [7,8].
Gracies proposes a plan built on both groups of signs [11]. Intensive motor training of the less overactive muscles should break the cycle of paresis, disuse and paresis. At the same time, stretch and focal weakening agents in their overactive, shortened antagonists should break the cycle of overactivity and contracture.
Movement also matters for the positive signs themselves. When weakness and the other negative signs keep a limb still, post-activation depression decreases, and this reduction of a normal inhibitory mechanism favors spasticity [4]. On the other hand, passive mobilization of the limb can restore post-activation depression and reduce or even prevent spasticity [4]. In short, keep the limb moving, and train what the patient has lost.
Finally, we show how to examine all of this in Spasticity Assessment: A Step-by-Step Clinical Exam.
Key points
- Upper motor neuron syndrome combines positive signs (muscle overactivity) and negative signs (weakness, loss of dexterity, fatigability).
- Negative signs appear immediately after the lesion. Most positive signs appear later, except the Babinski sign.
- Negative signs explain most of the disability. Spasticity is not related to weakness or loss of dexterity.
- Positive signs come either from hyperexcitable spinal reflexes (spasticity, clonus, spasms, Babinski sign) or from abnormal descending drive (co-contraction, associated reactions, spastic dystonia).
- A typical posture shows where to look, but the muscles involved vary between patients. Test each muscle.
- Train the weak muscles and keep the limb moving.
References
- Mayer NH, Esquenazi A. Muscle overactivity and movement dysfunction in the upper motoneuron syndrome. Phys Med Rehabil Clin N Am. 2003;14(4):855-883. doi:10.1016/s1047-9651(03)00093-7
- Sheean G. The pathophysiology of spasticity. Eur J Neurol. 2002;9(suppl 1):3-9. doi:10.1046/j.1468-1331.2002.0090s1003.x
- Thibaut A, Chatelle C, Ziegler E, Bruno MA, Laureys S, Gosseries O. Spasticity after stroke: physiology, assessment and treatment. Brain Inj. 2013;27(10):1093-1105. doi:10.3109/02699052.2013.804202
- Trompetto C, Marinelli L, Mori L, et al. Pathophysiology of spasticity: implications for neurorehabilitation. Biomed Res Int. 2014;2014:354906. doi:10.1155/2014/354906
- Gracies JM. Pathophysiology of spastic paresis. I: paresis and soft tissue changes. Muscle Nerve. 2005;31(5):535-551. doi:10.1002/mus.20284
- Li S, Francisco GE. New insights into the pathophysiology of post-stroke spasticity. Front Hum Neurosci. 2015;9:192. doi:10.3389/fnhum.2015.00192
- O’Dwyer NJ, Ada L, Neilson PD. Spasticity and muscle contracture following stroke. Brain. 1996;119(Pt 5):1737-1749. doi:10.1093/brain/119.5.1737
- Dromerick AW. Clinical features of spasticity and principles of treatment. In: Gelber DA, Jeffery DR, eds. Clinical Evaluation and Management of Spasticity. Humana Press; 2002:13-26. doi:10.1007/978-1-59259-092-6_2
- Pandyan AD, Gregoric M, Barnes MP, et al. Spasticity: clinical perceptions, neurological realities and meaningful measurement. Disabil Rehabil. 2005;27(1-2):2-6. doi:10.1080/09638280400014576
- Trompetto C, Currà A, Puce L, et al. Spastic dystonia in stroke subjects: prevalence and features of the neglected phenomenon of the upper motor neuron syndrome. Clin Neurophysiol. 2019;130(4):521-527. doi:10.1016/j.clinph.2019.01.012
- Gracies JM. Pathophysiology of spastic paresis. II: emergence of muscle overactivity. Muscle Nerve. 2005;31(5):552-571. doi:10.1002/mus.20285
- Kovalenko AP, Voznyuk IA, Misikov VK. Spasticity syndrome in cerebral pathology: evaluation and clinical models [in Russian]. Nevrologiya, Neiropsikhiatriya, Psikhosomatika. 2021;13(5):68-75. doi:10.14412/2074-2711-2021-5-68-75
