Motor Weakness

Differential Overview

Generalized

❑ Steroid myopathy

❑ Diabetic amyotrophy

❑ Polymyalgia rheumatica

❑ Polymyositis

❑ Myasthenia gravis

❑ Guillain-Barré syndrome

❑ Hyperthyroidism

❑ Muscular dystrophy

❑ Eaton-Lambert syndrome

❑ Metabolic myopathy

Paraparesis

❑ Trauma

❑ Multiple sclerosis

❑ Amyotrophic lateral sclerosis

❑ Guillain-Barré syndrome

❑ Epidural abscess

❑ Subacute combined degeneration

❑ Syringomyelia

❑ Aortic dissection

❑ Hysterical

Diagnostic Approach

Motor weakness should be distinguished from functional weakness due to systemic disease. Patients with true motor weakness will complain of difficulty performing specific tasks or a feeling of heaviness or stiffness in their limbs. Myopathy can be distinguished by proximal weakness (climbing stairs or combing hair), symmetrical distribution, absence of paresthesias and pain, or disturbance of bowel or bladder function. Proximal muscle weakness is more prominent in myopathy, distal weakness in peripheral nerve or anterior horn cell disease. Bulbar weakness, manifest as difficulty speaking and swallowing, is consistent with anterior horn cell disease or neuromuscular junction disorders. Ocular weakness occurs with myasthenia gravis and myotonic or oculopharyngeal dystrophy.

Acute generalized weakness with an onset over hours can be caused by low levels of potassium, calcium, sodium, magnesium, or phosphate; by botulism; or by viral inflammatory myopathy. Spasticity, manifest as increased tone and sudden release (“clasp-knife”), occurs with CNS lesions. Rigidity occurs with extrapyramidal disorders. Functional overlay should be suspected in the presence of ratcheting “give-away” weakness.

Peek sign: Orbicularis oculi weakness is observed on gentle eye closure. After initial complete apposition of the lid margins, they separate within seconds and the white of the sclera peeks through. Ice test: A glove finger filled with crushed ice is placed over the more ptotic eyelid for 2 minutes. An increase in opening of 2 mm or more is a positive result. Quiver eye movements: very fast, small twitch, jerk-like movements of the eyes upon changing the direction of gaze. Unintelligible speech: after prolonged speaking.

Clinical Findings

Steroid myopathy  Proximal muscle weakness develops in a patient taking chronic steroids.

Diabetic amyotrophy  Proximal weakness and atrophy of the legs, usually accompanied by anorexia, weight loss, and depression, occur in a patient with poorly controlled diabetes.

Polymyalgia rheumatica  Proximal muscle aches and arthralgias are often perceived as weakness. Fever, weight loss, and temporal arteritis are also part of the spectrum.

Polymyositis  Symmetrical proximal muscle weakness, with difficulty arising from a chair or climbing stairs, is the most striking finding. Difficulty swallowing may occur in 25%. Deep tendon reflexes are preserved.

Myasthenia gravis  The hallmark is rapid fatigability of the muscles with progressive weakness on repetitive use, and partial recovery after rest. Fatigability is especially seen in ocular muscles with resultant ptosis or diplopia. Dysphonia with a nasal voice, decreased volume with prolonged talking, and choking with nasal regurgitation, may occur.

Guillain-Barré syndrome  It is characterized by an ascending motor paralysis, areflexia, and mild sensory symptoms.

Hyperthyroidism  Weakness may be proximal or generalized. Fasciculations, bulbar weakness, and eye muscle involvement are present. Other signs of hyperthyroidism are usually evident, such as fine tremor, tachycardia, lid lag, and exophthalmos.

Muscular dystrophy  Early symptoms are difficulty climbing stairs and difficulty arising from a recumbent position (requiring use of the hands). Swayback, with a waddling gait due to gluteal weakness, and pseudohypertrophy of the calves may be seen. Types include: Duchenne (affects young boys); fascioscapulohumeral (onset 10 to 20 years); limb-girdle (affects shoulder and pelvic muscles); and myotonic dystrophy (onset is in early adulthood, with peripheral muscle wasting, frontal balding, and cataracts).

Eaton-Lambert syndrome  A paraneoplastic syndrome seen most often with small cell cancer of the lung. Weakness affects limbs more than cranial nerves and reflexes are disproportionately reduced.

Metabolic myopathy  Phosphofructokinase, lactate dehydrogenase, and muscle phosphorylase deficiency produce painful muscle cramps, weakness with exercise, and myoglobinuria (dipstick proteinuria). Acid maltase deficiency produces progressive weakness without myoglobinuria. Carnitine deficiency produces progressive weakness, increased by exercise.

Trauma  The history is obvious. There is a flaccid paralysis, and reflexes are absent.

Multiple sclerosis  Classic findings include diplopia and optic neuritis/atrophy, limb paresthesias, and internuclear ophthalmoplegia. Patchy, nondermatomal sensory symptoms separated in time and (neurological) space is the classic signature.

Amyotrophic lateral sclerosis  With lower motor neuron involvement, there is a slowly progressive asymmetric weakness, muscle cramping with movement, atrophy, and fasciculations. With corticospinal involvement, stiffness is the principal symptom, with hyperactive reflexes and spasticity.

Epidural abscess  Gradual onset of motor weakness occurs with back pain and fever.

Subacute combined degeneration  It is characterized by paresthesias in the hands and feet, dorsal column loss in the legs, tender muscles, weak legs, and spasticity with increased deep tendon reflexes and an upgoing plantar response.

Syringomyelia  It presents with spasticity of the legs, decreased deep tendon reflexes in the arms, decreased pain and temperature sense in the arms and thorax, and weakness or wasting in the arms.

Aortic dissection  Dissection of the spinal arteries will lead to sudden onset of inability to move a leg, but arm strength will be unaffected. There will be deep back pain, restlessness (so that a patient might seem to be fabricating symptoms), and a pulseless leg.

Hysterical  Normal deep tendon reflexes and la belle indifference are the main clues.

Pictures

Book Source Details

• Book Title: Field Guide to Bedside Diagnosis
• Author(s): David S. Smith
• Year of Publication: 2007
• Copyright Details: Field Guide to Bedside Diagnosis, Copyright © 2007 Lippincott Williams & Wilkins.

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Copyright Details: Field Guide to Bedside Diagnosis, Copyright © 2008 Williams & Wilkins.

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More About This Book: Title: Field Guide to Bedside Diagnosis Authors: David S. Smith Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 0-78178-165-5

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