CHAPTER 21

Diagnostic Evaluation of Adult Patients With Spasticity

Geoffrey Sheean

This chapter addresses the diagnostic approach to the adult patient with spasticity and associated forms of motor overactivity. It begins with a discussion of the upper motor neuron syndrome (UMNS) and the types of motor overactivity that can follow, of which spasticity is only one. Next, there is a discussion of other neurologic and nonneurologic disorders that could mimic these types of motor overactivities, a kind of phenomenological differential diagnosis. The chapter ends with an outline of the approach to making an etiological diagnosis of the cause of spasticity using history, examination, and investigations. It will focus on causes of spasticity that are not obvious.

UPPER MOTOR NEURON SYNDROME

The upper motor neurons (UMNs) are descending motor pathways that originate in the cortex or brainstem that influence excitability of the lower motor neurons (cranial motor neurons or anterior horn cells). Damage to the UMNs results in the UMNS, which has clinical features that are classified as either negative (loss of function or motor underactivity, eg, weakness) or positive (gain of function or motor overactivity). The forms of motor overactivity include spasticity, as defined elsewhere in this book, can be further grouped into hyperkinetic (involuntary movements) and hypokinetic (impairment of movement; see Table 21.1).

Thus, a variety of motor overactivities can be seen in the UMNS and so the differential diagnosis will depend on which are present (Table 21.2). For example, the differential diagnosis of spastic hypertonia (spasticity or spastic dystonia) includes all other causes of hypertonia, neurologic and musculoskeletal, and differs considerably from the differential diagnosis of, say, extensor spasms. Differentiating spastic hypertonia from other causes of hypertonia is based on velocity and length dependence and a pattern favoring extensors over flexors or vice versa, and a tendency to be greater in adductors and pronators than in abductors and supinators. Other clues that motor overactivity is caused due to an UMNS might come from associated positive features such as deep tendon hyperreflexia, an extensor plantar response, and from associated negative features, such as weakness in an UMN distribution, associated sensory loss, loss of superficial abdominal reflexes, aphasia, and so on. Finally, many diseases that cause UMN damage and spasticity can also cause extrapyramidal damage with resulting rigidity or dystonia; so the clinician should be on the lookout for combinations of motor overactivity.

CAUSES OF SPASTICITY

Very often, the cause of spasticity in an adult is already apparent because it follows a known event, such as a stroke, head injury, spinal cord injury, or episode of anoxia, or it occurs in the course of a known disease, such as multiple sclerosis (MS). If not, the cause is frequently found with neuroimaging of the brain or spinal cord with MRI, which reveals spinal cord compression, a brain or spinal cord tumor, hydrocephalus, myelomalacia, plaques of MS, or diffuse demyelination of a leukodystrophy, and so on. This chapter deals with causes of spasticity that are not so readily apparent as well as uncommon causes that have nonspecific features on neuroimaging (Table 21.3).

Spasticity usually does not develop rapidly but rather gradually. The sudden onset of something that appears to be spasticity is probably some other type or motor overactivity, for example, tetanus, strychnine poisoning, or decerebrate rigidity. Furthermore, most of the occult causes of spasticity are slowly progressive disorders.

TABLE 21.1

UMNS, upper motor neuron syndrome.

^aActive or passive.

History

History taking might reveal a family history of a spastic disorder (eg, hereditary spastic paraplegia [HSP]) or another genetic neurologic disorder that can cause spasticity. Previous transient neurologic symptoms might suggest MS. Sensory symptoms would point away from pure motor syndromes, such motor neuron disease and (hereditary) progressive spastic paraplegia. A history of electrocution or irradiation might be relevant, as would a history of recent carbon monoxide or organophosphate poisoning. A history of bariatric surgery, gluten-intolerance, or a strict vegan diet (vitamin B₁₂) could suggest a nutritional cause. A history of tick bite and a rash could point to an infectious cause (Lyme disease). Alcoholism can result in spasticity in several ways. A history of hepatitis B or C exposure, or even the known presence of cirrhosis, especially with a portosystemic shunt (spontaneous or surgical), might suggest a diagnosis of hepatic myelopathy. Adults with phenylketonuria (PKU) who abandon their diet can later present with spasticity. A history of spinal injury in the past could raise concern for a delayed posttraumatic complication. A history of repair of myelomeningocele or other congenital abnormality in childhood would make one consider a tethered cord. Some unusual causes of spasticity have symptoms of autonomic dysfunction or dementia. The presence of urinary or fecal incontinence would also narrow the field of possibilities, at the very least by suggesting myelopathy.

TABLE 21.2

MS, multiple sclerosis.

Examination

The examination should include testing of muscle tone at different velocities of muscle stretch to determine whether the hypertonia is velocity dependent or not. Observation of whether hypertonia affects some muscle groups more than their antagonists (eg, wrist flexors more than extensors) should be made to help distinguish spasticity from rigidity. The clasp-knife phenomenon might be present in the elbow flexors or quadriceps, for example, rapid flexion of the knee proceeds until it soon meets sudden strong resistance (a “catch”) slowing movement, but under a continuing stretching force, the resistance gradually “melts away.” Brisk deep tendon reflexes and clonus at the knees or ankles are supportive of a UMNS but can be physiological or due to other disorders such as hyperthyroidism. Similarly, radiation of reflexes, crossed adductor reflexes, and Hoffman’s sign only indicate hyperreflexia, which is not necessarily pathological. Clonus at the wrists can be difficult to distinguish from the cog-wheeling of parkinsonism but the latter would be associated with rigidity rather than spasticity. The absence of superficial abdominal reflexes supports a UMNS but can be absent in multiparous women, obese people, and those with extensive abdominal surgery. Extensor toe responses, whether obtained by plantar stimulation (Babinski sign) or otherwise, indicate pathology of the corticospinal tract: an astute observer might notice that pulling off the patient’s socks elicits an extensor great toe response. There may or may not be evidence of the negative features of the UMNS, such as an UMN pattern of weakness. Fine finger movements might be impaired and there may be a pronator drift in the outstretched upper limbs.

TABLE 21.3

ALS, amyotrophic lateral sclerosis; AVM, arteriovenous malformation; CNS, central nervous system; HTLV, human T-lymphotropic virus; PLS, primary lateral sclerosis; PNPLA6, patatin-like phospholipase domain containing 6; SCA, spinocerebellar ataxia type.

Active movement may elicit spastic cocontraction, for example, cocontraction of the finger or elbow flexors when attempting extension. Standing and walking might reveal the abnormal posturing of spastic dystonia (eg, the “hemiplegic posture or gait” or the “spastic diplegic gait”). Some patients do not have spasticity (at rest) and only develop motor overactivity during active movement.

Clues might also be obtained from the topography of the spasticity. Affliction of the lower limbs only suggests a spinal cord lesion below T1 or a parasagittal frontal lesion. A hemibody pattern suggests a lesion above C5, whereas facial or bulbar involvement places the lesion above the brainstem, as does a brisk jaw jerk.

Involvement of other neurologic systems and other bodily systems can also yield clues to the etiology (Table 21.4).

Investigation

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