Motor neuron disease encompasses a group of progressive neurologic disorders that destroy cells responsible for the control of essential muscles. The disorders are characterized by progressive weakness, muscle atrophy and fasciculation, spasticity, dysarthria, dysphagia, and respiratory compromise. A 66-year-old male presented to the emergency department with progressive dyspnea and, ultimately, respiratory failure. In spite of extensive cardiopulmonary evaluation, a cause could not be identified except aging. After complete history taking, physical and neurologic examination, motor neuron disease was suspected at last. Thus, elderly patients with dyspnea in the emergency department could have hidden diseases beyond the normal aging process.
Motor neuron disease (MND) is a heterogenous group of disorders those selectively affect upper or lower motor neurons, or both. Sporadic amyotrophic lateral sclerosis (ALS) accounts for approximately 80% of all cases of acquired motor neuron disease, whereas the remaining 20% of patients have either only lower motor neuron signs or a familial form of ALS (FALS). The 80% of patients who have sporadic ALS present with spasticity, hyperreflexia, and Babinski's sign in the setting of progressive muscle wasting and weakness.
A previously healthy, 66-year-old male patient presented to the emergency department (ED) for evaluation of progressive dyspnea, which had begun 3 months prior to presentation. His family and past medical history were not remarkable except for benign prostatic hyperplasia. He was a non-smoker and denied alcohol use. The patient denied any chest pain, rhinorrhea, cough, sputum production, or fever. The dyspnea was aggravated by exercise and relieved with rest. On examination, he was alert, but appeared thin, scaled and pale. His vital signs included a blood pressure of 143/73 mm Hg, heart rate of 84/min, respiratory rate of 18/min, temperature of 36.4℃, and an oxygen saturation of 89% measured by pulse oximeter. The conjunctivae were pink. The lungs were clear to auscultation without wheezes, rales, or rhonchi. There was no abnormal heart sound or pitting edema at the ankles. The abdomen was flat and had normal bowel sound.
The initial laboratory evaluation showed an arterial blood gas of pH 7.347, PCO2 66.6 mm Hg, PO2 63.3 mm Hg, and HCO3- 31.3 mmol/L. Point-of-care testing included creatine kinase 133 IU/L, creatine kinase-MB 6.8 ng/mL, troponin-I 0.01 ng/mL, B-type natriuretic peptide 12, and D-dimer 0.03. Blood chemistry analysis and complete blood count were normal. Influenza antigen test was negative. A chest radiograph showed atelectasis in the right upper lung field (
Despite oxygen treatment with an 8-liter oxygen mask with reserved bag, the dyspnea became worse, and the oxygen saturation dropped to 86% after 3 hours. Computed tomography of the chest identified bronchiectasis in right upper lung field associated with bronchopneumonia (
The patient's history was reviewed, and the physical examination was repeated to look for additional information. The patient reported a 10 kg weight loss over the last year and had been bedridden for generalized weakness. The neurologic examination disclosed dysarthria, mild bilateral lower extremity weakness, and calf muscle atrophy. The dyspnea progressed to respiratory failure after 6 hours from the time of presentation in the emergency department, and intubation was required. Further investigations with nerve conduction study and electromyography demonstrated widespread denervation without any electrophysiologic abnormal findings of peripheral neuropathy. Finally, the patient was discharged with tracheostomy and home ventilator after several weeks' antibiotics treatment, and followed up via out-patient department.
MND refers to a group of diseases that affect the cells that control voluntary muscle activity. In the United States, MND is more commonly referred to as ALS or Lou Gehrig's disease (to avoid confusion, the annual scientific research conference dedicated to the study of MND is called the International ALS/MND Symposium). ALS/MND refers to a specific subset of pathologically identical diseases. Forms of motor neuron disease include FALS, spinal muscular atrophy, bulbospinal muscular atrophy, anterior poliomyelitis, sporadic ALS, and primary lateral sclerosis.
Currently, no cures exist for MND. The only drug that affects the course of the disease is riluzole, which blocks the effect of the neurotransmitter glutamate. Riluzole generally extends the lifespan of an MND patient by a few months.
The incidence of MND is approximately 1 to 5 in 100,000 people, and men experience a slightly higher incidence than women. Symptoms usually present between the ages of 50 and 70 years, and include progressive weakness, muscle wasting, muscle fasciculation, spasticity or stiffness in the arms and legs, and overactive tendon reflexes. Neurologic examination identifies specific signs associated with upper and lower motor neuron degeneration. Signs of upper motor neuron damage include spasticity and brisk reflexes. Pathologic reflexes, including Hoffmann's sign in the fingers and the Babinski sign, are frequently seen. Signs of lower motor neuron damage include weakness, fasciculations, and muscle atrophy. These signs can occur in any muscle group, including the arms, legs, torso, and bulbar region.
Approximately 5% of cases with MND present with respiratory weakness without significant limb or bulbar symptoms.
In conclusion, primary care physicians are often quick to conclude that motor power has weakened due to aging, only after usual history taking without cautious physical and neurologic examination. However, physicians who encounter patients with dyspnea in ED have to rule out pulmonary and cardiac dysfunction above all. If the clinical feature could not be explained, a differential diagnosis should be maintained, including neurologic disorders, which can frequently be overlooked in the elderly.
No potential conflict of interest relevant to this article was reported.
Chest X-ray. Right upper lung bronchopneumonia (arrow).
Electrocardiography.
Enhanced chest computed tomography showed bronchiectasis with mucous plugging in right upper lobe. Otherwise, there was no remarkable finding.