When we talk about muscle weakness we refer to the decrease or reduction of the muscle strength of a particular muscle or a certain muscle group.
There are many and varied causes of muscle weakness and the treatment will depend on the specific origin.
For muscle movement to occur voluntarily, a signal is generated in the brain and follows a specific pathway to the muscle for movement. According to these topographic levels, the cause of muscle weakness can be located at 4 different levels:
· Medullary (spine)
· Peripheral nerves
· Muscular itself, at the junction of nerves and muscles
In the same way, the approach is different, if the condition is located in an isolated or specific muscle or muscle group, or it is generalized weakness.
Here we can differentiate many causes
Among the most common causes of generalized muscle weakness are: hypotrophy or atrophy due to long periods of lack of movement, disorders caused by drugs or electrolytes or alcoholism.
In the case of localized muscle weakness, the list is longer and includes a large number of different pathologies.
At this point, medical evaluation is essential to be able to identify the origin of the problem and establish a specific treatment.
Muscle weakness can be classified according to its severity in 4 levels.
In this sense, disorders associated with muscle weakness, which is the objective loss of muscle strength, must be differentiated from terms such as asthenia and fatigue.
We speak of asthenia when there is a feeling of fatigue without lack of muscle strength. Fatigue is the inability to continue a sustained activity, nor is it objective muscle weakness.
There are clinical pictures that present with asthenia or fatigue and additionally muscle weakness. This generates a lot of confusion, because in the course of the same disease variable degrees of muscle weakness associated with fatigue or asthenia, among other symptoms, can be seen.
Causes of primary muscle weakness
Endocrinological causes usually present with many symptoms in different organs, so their diagnosis is made through physical examination and laboratory determination with hormonal stimulation tests or direct measurement of certain hormones.
They tend to improve after starting treatment, either hormonal or surgical restoration. In many cases they require lifelong treatment unless it is resolved surgically.
· Adrenal insufficiency or Addison's disease, decreased production of glucocorticoids.
· Hyperparathyroidism; produce alterations in calcium levels, which cause significant muscle changes.
· Hypokalemia, from any cause, due to low potassium levels, associated with Addison's disease or other causes.
· Hyperthyroidism, excess thyroid hormone.
· Amyotrophic lateral sclerosis (ALS), an incurable chronic disease that generates peripheral muscle weakness without brain or cognitive alteration. Its origin is unknown and so far it has not been treated. Symptoms of additional diseases that occur over time are being treated. Support is provided for both feeding and ventilation in advanced cases.
· Guillain-Barre syndrome, proximal muscle weakness secondary to infectious processes. It produces a weakness that generates complete prostration. Its cause is of immunological and infectious origin. The weakness is usually completely reversed after medical treatment under hospitalization, although it can take months to recover.
· Multiple sclerosis, myelin disease, of unknown origin, has several clinical presentations. Currently there are several types of treatment that prevent the progression of the disease and stop the process of muscle weakness.
· Pinched nerve (for example, caused by a herniated disc in the spine). In these cases, the transmission of the nerve impulse to the corresponding muscle group is interrupted. The weakness is localized, so it is easier to locate the origin.
· Stroke: depends on the affected area at the brain level, which controls a certain group of muscles or limbs in the body. The weakness can vary from mild to severe and its recovery depends on the general condition of the patient, the size of the cerebral affection and the promptness of medical attention after the vascular episode of origin.
· Muscular dystrophy (Duchenne).
· Myotonic dystrophy.
· Myasthenia gravis: It is perhaps the most common and emblematic of all neuromuscular disorders that typically produce muscle weakness. It can be located only on the eyelid, for example, generating ptosis or drooping of the eyelid. It can be generalized with weakness that disables walking and normal activities, until it affects the respiratory muscles. Its precise cause is not known, an autoimmune origin has been established. It is known that there is an alteration in acetylcholine, which is a neurotransmitter that allows communication of the stimulus from the nerve to the muscle. In the case of women, they usually start the disease between the ages of 30 and 40, while men tend to develop it more frequently, after 60 years of age. There are a number of alternatives for the treatment of this condition, from immunosuppressants,
· Spinal cord injuries.
Rheumatological causes, of autoimmune origin, that improve with immunosuppressive treatment or steroids
· Systemic lupus erythematosus.
· Rheumatoid arthritis.
Intoxication: it is necessary to determine the blood levels of the toxin, limit the exposure and apply treatment, they are usually reversible.
· Poisoning (insecticides - organophosphates)
· Shellfish poisoning
There are a number of viruses and infectious agents that can cause muscle weakness. The clinical presentations vary according to the infectious agent involved and the diagnosis is made basically when there are other signs than the underlying disease or the antecedent of the recent infectious process is known
Pharmacological causes: proper questioning may rule out the possible relationship of drugs or their combinations in patients with generalized muscle weakness. This background should be investigated quite carefully. Here are some of the medications involved:
· Statins: rosuvastatin, simvastatin, pravastatin, and atorvastatin
· Cimetidine (H3 blocker, gastric acid).
· Chemotherapy (some).
· Retroviral agents such as AZT and lamivudine.
· Antibiotics such as penicillin and sulfonamides.
· Diuretics such as furosemide.
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