Muscle Weakness

Introduction

The operational setting often involves strenuous missions.  Muscle weakness must be differentiated from muscle fatigue merely due to physical exertion. 

Many who complain of weakness will test normally on an objective muscle strength exam. Weakness can also be a global complaint associated with many systemic illnesses such as:

• Cardiopulmonary disease

• Anemia

• Infections

• Rheumatologic diseases

• Metabolic diseases

• Malignancies

• Depression

An important point is that patients with systemic disease usually complain of a vague weakness, whereas those with true muscle weakness will complain of the inability to perform a task, such as gripping, pulling or pushing objects, combing hair, or rising to a standing position.  Muscle pain is a non-specific sign that could indicate muscle inflammation seen with myositis or rhabdomyolysis; however muscle pain can also be seen with muscle cramps after over-exertion, dehydration, and fibromyalgia.  Muscle weakness also may be associated with neurological or neuromuscular disease, such as:

• Spinal cord lesions or injury

• Demyelinating diseases

• Nervous system inflammation

• Infection

• Malignancy

• Lower motor neuron disease

• Disease of the neuromuscular junction.

History

Try to determine if the complaint of muscle weakness is related to physical exertion, a systemic process, or a condition of true muscle weakness.   Pattern your questioning by starting with muscle then working backwards, first regarding diseases of the muscle, then the neuromuscular junction, then the peripheral and central nervous system, then finally about systemic or psychiatric conditions. 

• Has the patient just exerted him/herself?  Determine the hydration status.  How much water was consumed during the activity?  Rhabdomyolysis frequently occurs in the setting of exertion while dehydrated.  

• Has the urine changed from a yellow to a brown or red, indicating possible muscle breakdown?   

• Is there a specific function the patient finds difficult?  

• Determine the pattern of weakness.  Is the weakness symmetric or asymmetric?  Difficulty lifting the arms or combing the hair as well as difficulty rising to a standing position indicates possible proximal muscle pathology if these muscle groups have not been recently exerted.    

• Has the patient recently eaten undercooked pork, which is associated with trichinosis?  

• Does the weakness occur progressively during short light exertion of muscle groups as seen in Myasthenia Gravis?  

• Symptoms of tingling, numbness, or tremors indicate possible neurological disease.  

• Has there been a substantial change in behavior to suggest a possible intracranial process?  

• Ask about exercise tolerance and shortness of breath, chest pain, wheezing, leg swelling or blood loss to assess for asthma, heart disease, or anemia.  

• Weight loss, fevers, night sweats, and rash may indicate a systemic inflammatory, infectious, or neoplastic process.  

• Assess the emotional and psychiatric state of the patient to assess for depression, adjustment disorder, or other such conditions.

Physical Exam

A full neurological exam is warranted with emphasis on the motor exam.  All muscle groups should be tested for strength and pattern of weakness including specific muscle groups, symmetry, proximal vs. distal, and tenderness to palpation.  Other things to look for include abnormal tone, atrophy, fasiculations, tremors, coordination, abnormal reflexes, and sensory changes, all of which indicate possible neurological involvement.  Also look for fatigue with light activity (i.e. blinking) to suggest Myasthenia Gravis.

In cases of global weakness, abnormal chest findings such as crackles, wheezing, diminished breath or cardiac sounds, and murmurs could point to a cardiopulmonary process.   Pallor, blanched conjunctivae, and tachycardia are associated with anemia.  Excessive sweating, weight loss, jitteriness, and tachycardia make hyperthyroidism possible, whereas hypothyroidism would be suggested by weight gain, dry skin, and sluggishness.  Weight loss, cachexia, fever, and lymphadenopathy could indicate a variety of inflammatory, infectious, or neoplastic processes.

Labs and Other Tests

If available, muscle enzymes (CK, aldolase) and urinalysis (to check for myoglobinuria) to assess for rhabdomyolysis;  CBC, ESR, ANA, TSH, electrolytes including calcium, magnesium, and phosphorus plus renal function (derangements of which can lead to muscle weakness) as indicated to assess for anemia, various inflammatory processes, metabolic and renal disease.   If cardiopulmonary disease is suspected, a chest x-ray and EKG may be warranted.   

Plan

If the muscle weakness is due merely to over-exertion and no clinical disease is indicated by history, physical, or laboratory/radiological testing, let the patient rest.  Weakness will most likely dissipate with proper rest.

If rhabdomyolysis is present, rest and rehydration are paramount.  Often, any decline in renal function due to rhabdomyolysis will normalize with proper hydration.  Mild renal dysfunction that does not normalize should be discussed with a specialist or referred.  Severe renal dysfunction should be referred immediately to the nearest medical center to preserve kidney function.

If inflammatory muscle disease, neuromuscular junction disease or neurological disease is suspected, the patient should be restricted from further activity and MEDEVAC’d for further evaluation which may include further specialized lab testing, neurological imaging with CT or MRI, EMG, or nerve conduction studies.  Depending on the clinical scenario, the patient may require assistance from specialists in Internal Medicine, Rheumatology, Neurology, or Neurosurgery.  Cardiopulmonary conditions should be stabilized and then medevac’d for further evaluation.  If the weakness is a symptom of depression, adjustment disorder, or other psychiatric condition, proper counseling is warranted with possible pharmacological treatment if indicated.  

This section provided by LT Arthur S. Pemberton, MC, USNR, Naval Medical Center Portsmouth

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