A 67-year-old man is referred to a neurologist by his general practitioner (GP). His symptoms are of weakness and wasting of the muscles of his left hand. He has noticed the weakness is worse after using his hand, for example after using a screwdriver. He has also noticed cramps in his forearm muscles. His speech is slightly slurred and he has started choking after taking fluids. Past medical history is notable for hypertension for 15 years and a myocardial infarction 3 years previously. Medication consists of simvastatin, aspirin and atenolol. He is a retired university lecturer. He lives with his wife and they have two grown up children. He is a non-smoker and drinks a bottle of wine a week.
Examination Blood pressure is 146/88mmHg. There are no abnormalities to be found in the cardiovascular or respiratory systems or the abdomen. There is some wasting of the muscles in the upper limbs, particularly in the left hand. There is some fasciculation in the muscles of the upper arms bilaterally. Power is globally reduced in the left hand, and also slightly reduced in the right hand. Muscle tone is normal. The biceps and triceps jerks are brisk bilaterally. There is no sensory loss. There is slight dysarthria.
Questions • What is the diagnosis? • What is the prognosis?
ANSWER
This man has motor neurone disease. This is a degenerative disease of unknown cause that affects the motor neurones of the spinal cord, the cranial nerve nuclei, and the motor cortex. The disease usually presents between the ages of 50 and 70 years. Weakness and wasting of the muscles of one hand or arm is the commonest presentation. Weakness is most marked after exertion. Painful cramps of the forearm muscles are common in the early phases of the disease. Patients may present with lower limb weakness or with dyarthria or dysphagia. The characteristic physical sign of this condition is fasciculation, which is an irregular rapid contraction of segments of muscle, caused by denervation of the muscle from a lower motor neurone lesion. Reflexes can be brisk due to loss of cortical motor neurones. There is no sensory loss. In advanced cases diagnosis is easy, but early cases are more problematic. Limb weakness worsening with fatigue may be confused with myasthenia gravis. Dysphagia and dysarthria in the elderly are much more commonly due to the pseudobulbar palsy of cerebrovascular disease. Cervical myelopathy is another common cause of wasting and fasciculation of the upper limbs without sensory loss. Brachial plexus lesions from trauma or invasion by an apical lung tumour (Pancoast tumour) may affect one arm. A predominant motor peripheral neuropathy causes a symmetrical pattern of weakness and reflexes are reduced. Unfortunately motor neurone disease is a progressive and incurable condition. Patients tend to develop a spastic weakness of the legs. Bulbar palsy causes dysarthria and dysphasia. Sphincter function is usually not affected. Intellect is generally not affected. There is no curative treatment for this condition. The mean duration of survival from presentation is between 2 and 4 years. The patient and his family will have to be told of the diagnosis and prognosis. Support must be given by a multidisciplinary team. As the disease progresses and speech deteriorates communication may be helped by using computers. A feeding gastrostomy may be required to enable adequate calorie intake. Noninvasive ventilation can be used to help respiratory failure, but death usually occurs from bronchopneumonia.