What Are Muscle Biopsy and Clinical and Laboratory Features of Neuromuscular Disease?

A muscle biopsy is used to diagnose a neuromuscular disorder like Parkinson's, multiple sclerosis, or Huntington's disease.

A biopsy is an examination of tissue removed from a living body to discover the presence, cause, or extent of a disease. A biopsy of skeletal muscle tissue (muscle biopsy) is a diagnostic procedure used in the evaluation of neuromuscular diseases and patients with suspected myopathy. 

A muscle biopsy is also sometimes indicated for diagnosing various systemic disorders that also present with skeletal muscle tissue pathology. The surgical procedure to obtain a muscle biopsy is relatively simple and poses little risk to the patient.

When a clinical diagnosis of a neuromuscular disorder is considered, a muscle biopsy is often required for definitive diagnosis. It also helps diagnose other systemic disorders that affect the muscles.

Neuromuscular disorders affect the nerves, muscles, or neuromuscular functioning. Some examples of neuromuscular disorders are

• Parkinson’s disease,
• Huntington’s disease,
• multiple sclerosis, etc.

Skeletal muscles are mostly affected. Skeletal muscles are muscles that are connected to the skeletons (bones), forming the mechanical system of the body that helps in movement and voluntary actions. 

Risk factors for neuromuscular disorders could be genetic, vitamin B12 deficiency, heavy metal/chemical poisoning, or autoimmune (when the body’s immune system attacks its own cells). Besides muscle biopsy, other diagnostic tests such as electromyography, genetic testing, and blood and radiological tests may be performed.

Patients with neuromuscular disorders present the following signs and symptoms:

• Muscle pain
• Spasms
• Paresis (muscle weakness)
• Rigidity
• Paralysis
• Involuntary movements (tremors, tightness in muscles, and uncontrollable tics)
• Muscle wasting
• Inability to extend the joints
• Night sweats
• Decreased lung function affecting breathing
• Difficulty swallowing

The procedure is usually performed with local anesthesia. General anesthesia may be used in children or anxious and uncooperative adult patients. A biopsy of a clinically involved muscle is important. 

Different disorders affect different groups of muscles with varying severity. Some disorders may have a patchy distribution rather than being diffusely distributed in the affected muscles. Hence, it occasionally happens that even if an affected muscle is biopsied, the biopsy might not sample the pathology.

The selection of a muscle to be biopsied is based on the provisional diagnosis based on the history and clinical assessment by the doctor. For example, if polymyositis is suspected, a proximal muscle that is likely involved in the condition may be the best choice for a biopsy.

When possible, a biopsy is usually performed on a mildly symptomatic muscle, but not on the one that is too weak or wasted because this may result in obtaining a sample of an end-stage muscle. 

In an end-stage muscle, the loss of myofibers is severe, hence does not help in diagnosis of pathology. The biopsy sample is then sent to the pathologist for evaluation.

The surgical procedure to obtain a muscle biopsy is relatively simple and poses little to no risk to the patient.

Uncommon complications are:

• infection and
• a possibility of infection after the procedure.