Somatosensory evoked potentials in patients with amyotrophic lateral sclerosis MARK A. MAC NEALY, DD. Dayton, Ohio LOUIS E. RENTZ, D.O. Madison Heights, Michigan and lateral columns, in addition to degeneration of In this study the somatosensory the crossed and uncrossed pyramidal tracts. It is evoked responses recorded from the not known whether this is caused by demyelination skin surface from seven patients with or to degeneration of axons.3 amytrophic lateral sclerosis (ALS) The motor neurons are divided into upper and and an age-matched control group lower groups. The upper motor neurons have both were compared. In the measurement direct and indirect corticospinal pathways. The di- of each wave form there was overall rect corticospinal tract arises primarily in the less reproducibility and more motor cortex and descends to the medulla, where variability in the ALS group than in approximately 90 percent of the fibers decussate to the controls. Analysis of the findings form the contralateral corticospinal tract. The re- and possible clinical significance maining 10 percent of the fibers form the uncrossed are considered. anterior corticospinal tract. The indirect corticos- pinal pathways originate in a location similar to that of the direct corticospinal tract but synapse in a variety of brainstem structures before their im- pulses reach the spinal cord. These brainstem Amyotrophic lateral sclerosis (ALS) is a disease of structures include the red nucleus, medial and lat- the motor neurons. It is a fatal, degenerative eral vestibular nuclei, medial pontine, medullary neurologic disease involving the motor cortex, cor- reticular formation, and the deep layers of the ticospinal tract, and anterior horn cells of the spi- superior colliculus. nal cord. There is no known etiology. The pathways from the brainstem include the Motor neuron disease has been classified among rubrospinal, olivospinal, tectospinal, vestibular, the so-called abiotrophic conditions affecting the and reticulospinal tracts. These tracts influence central nervous system. These are diseases in the lower motor neuron (final common pathway), which genetic factors are believed to result in the which consists of a cell body located in the anterior gradual and premature death of cells ordinarily grey column of the brainstem or spinal cord and the destined to live many more years. The concept of axon passing by way of the peripheral nerves to the abiotrophy suggests that there are premature dete- motor end-plates of the muscles. The lower motor rioration and death of one or more systems of cells neurons (anterior horn cells) are formed through- that make up the central nervous system. The ear- out the spinal cord and in the brainstem (cranial liest degenerative changes occur in the most pe- nerves III-VII and IX-XII).4 ripheral part of the longest cell process and pro- Thus, motor neuron disease is divided into three gressively ascend toward the cell body. In ALS, syndromes, according to which portion of the sys- these changes can be recognized on microscopic ex- tem is affected, the anterior horn cells, the nuclei of amination by the presence of wallerian degenera- the cranial nerves, or the pyramidal tracts. Pro- tion of the lateral and anterior corticospinal tracts. gressive spinal muscular atrophy, progressive bul- They may be seen at all levels of the spinal cord and bar palsy, and ALS are all part of the same disease may be traced upward in the pyramidal system, process.5 The pathologic evidence suggests that sometimes as far as the internal capsule.2 ALS and parkinsonian dementia, which are highly Above the latter level the tracts fan out widely prevalent in Guam and the Mariana Islands, are toward their origins in the precentral and post- distinct local diseases. central gyri. The changes may be severe enough The clinical symptomatology of ALS includes the to be obvious without formal cell counts. More- clinical components of progressive muscular atro- over, in the spinal white matter there is often phy and progressive bulbar palsy. Also present are a diffuse loss of stainable myelin in the anterior signs of corticobulbar and pyramidal tract in- Somatosensory evoked potentials in patients with amyotrophic lateral sclerosis 39/93 volvement including hyperreflexia, palmomental legs as one of the first signs of upper motor neuron responses, and the Babinski signs. Occasionally involvement. Hyperreflexia may be manifested by these may be masked by muscular atrophy. ankle clonus, which is sometimes experienced by ALS is the major form of motor neuron disease. It patients when pressing the foot firmly, such as in involves both the pyramidal tract and anterior applying the brake of a car. horn cells. The annual death rates worldwide are 1 Bulbar involvement causes the patient to have per 100,000; the prevalence is from 4 to 6 per difficulty with both swallowing and speaking. 100,000.6 Recently, the figures for the years 1925 From 9 to 26 percent of patients with motor neuron through 1977 in the population of Rochester, Min- disease have dysarthria or dysphasia and in nearly nesota, demonstrated an annual average incidence 100 percent the mouth, the pharynx, or both are of 1.76 per 100,000 population. The male-female involved eventually" The patient may complain ratio was 1.1 with an incidence rate of 1.6. The that solid foods lodge at the back of the throat. This median age of onset was 66 years, with the median is because he is unable to effectively initiate swal- survivalship of 22.5 months. lowing. This leads to an accumulation of saliva in The clinical symptoms of ALS are associated with the pharynx and choking spells result. Speech is degeneration of the motor nerve cells through- often difficult to evaluate because it reflects out the nervous system. Spasticity and hyperre- characteristics of both upper and lower motor flexia reflect the damage to the upper motor neuron damage. When the upper motor neuron neurons. The relentless wasting and weakness of changes predominate, the speech has a forced those muscles which lose their nerve supply reflect monotonous quality. This progresses until, in the the lower motor neuron component. late stages, the patient may be completely mute or Unfortunately, various clinical descriptions do only able to utter a strange moaning sound. not always clearly reflect the truly terrifying as- Pseudobulbar affect associated with the forced pects of this disease. This is more dramatic in the laughter or inappropriate crying may be present in acute form of the disease. ALS patients develop a some patients. However, before the diagnosis of rapidly progressive weakness of the arms and legs pseudobulbar affect is made, it must be remem- associated with an inability to swallow or speak; bered that ALS is an appalling disease and the yet, even to the end (typically caused by respiratory patient may quite understandably burst into tears failure or acute aspiration), the mind remains on occasion. clear. It is not surprising to see medical students The facial muscles are occasionally weak, how- and even physicians panic when they develop ever, with no extraocular palsies. In fact, the occur- common benign fasciculations interpreted by them rence of weakness in the extraocular muscles as early signs of this disease. would make one doubtful about the diagnosis of Patients with bulbar palsy occasionally may ex- motor neuron disease. Bladder and bowel difficul- perience rapid changes in affect leading to involun- ties likewise are seldom seen. Urinary inconti- tary outbursts of crying or laughter completely un- nence may occur; however, its basis is not clear. related to their mood or surroundings. These emo- The relentless course of the disease is mirrored tional outbursts can be quite disconcerting to those by the increasing helplessness in the patient. Con- around them. Certainly, these patients are fearful, finement to a wheelchair occurs within 12 to 18 angry, and often depressed, which can be a frustrat- months. In the end, the patient is bedridden, un- ing aspect of their care both for their families and able to move anything but the eyes, unable to speak themselves. The early symptoms are caused by a or swallow. Anoxia, caused by respiratory failure is patchy distal distribution of weakness. The hands evidenced by nightmares, confusion, and ulti- may be clumsy, resulting in difficulty in the per- mately death. ALS is one of the rare conditions in formance of fine motor skills such as sewing or which atrophic, weak muscles are associated with handling small parts. Occasionally the patient may hyperreflexia. Preservation of the superficial ab- complain of increased episodes of tripping, caused dominal reflexes is not unusual. Atrophy of the by a mild foot drop. Difficulty with chewing or tongue may occur with indentations caused by the swallowing also may be noted. Myoclonic jerks may teeth becoming noticeable along the edges. In addi- develop during sleep, and night cramps with pain tion, fasciculations of the tongue may also be noted. in the calf or thigh muscles is an early symptom. Paresis of the posterior pharyngeal wall and pal- Fasciculations may be more noticeable at night and atal weakness also may be seen. Weakness of both may interfere with sleep. The relative absence of neck flexors and extensors occurs as well. The fasciculations has been reported to reflect a slow diagnosis of motor neuron disease can be made with progression of the disease.6 It is not unusual for the some assurance if weakness, wasting, and fascicu- patient to experience a heaviness or stiffness of the lations are found in three or more extremities asso- 40/94 Sept. 1981/Journal of AOA/vol. 81/no. 1 ciated with increased reflexes. If bulbar signs are and forearm might have a local lesion of the bra- present, the diagnosis is even more certain.