During a muscle biopsy, physicians remove muscle tissue from skeletal muscles for the diagnosis of neuromuscular diseases, for example, in the presence of myopathies. Another task of muscle biopsy is the examination of the preserved tissue material. Closely related specialties are neurology, neuropathology, and pathology.
What is muscle biopsy?
During a muscle biopsy, physicians remove muscle tissue from skeletal muscles to diagnose neuromuscular diseases, such as the presence of myopathies. Various disease processes can cause pain or muscle weakness. These abnormalities lead to permanent problems and diseases of connective tissue, nervous system, vascular system or musculoskeletal system. In the field of sports medicine, muscle biopsies are performed to gain insight into muscle metabolism during and after physical exertion. Muscle biopsy is induced in cases of atypical or unusual complaints or when symptoms are predominantly confined to the trunk (proximal) muscles. Tissue biopsy is an important medical tool for differential diagnostic findings in suspected ALS (degenerative disease of the motor nervous system). However, it is not necessary in every case. Findings regarding changes in muscle tissue, particularly in second motor neuron disease, are based on the evaluation of frozen muscle sections that are routinely stained and examined for the presence of specific enzymes using specific reagents. In ALS, only mildly weakened muscle is selected for biopsy. Usually, the four-headed thigh muscle (Musculus quadriceps), the anterior lower leg muscle (Musculus tibialis anterior), or the upper arm flexor muscle (Musculus biceps) are used for biopsy. Muscles that are damaged by non-specific effects such as direct trauma, entrapment of a nerve, or a nerve root lesion are unsuitable. A muscle that is injured, has been the subject of an EMG within the past three weeks, or has recently been the site of frequent injections is unsuitable for performing the biopsy.
Function, effect, and goals
The goal of muscle biopsy is to ensure the initiation of appropriate treatment after diagnosis. It allows physicians to detect abnormalities in the musculoskeletal system under investigation. A muscle biopsy is uncomplicated and is performed under local anesthesia. For this procedure, the physician selects a muscle that is clearly diseased, but not yet completely fatty or atrophic. The clinical aspect or the results of performed examinations (sonography, magnetic resonance imaging) are the basis for the selection of the appropriate muscle. If the selection of the tissue cannot be conclusively clarified, an electromyography (EMG) or an MRI is used. To avoid erroneous findings, the biopsy is not performed in areas where EMG electrodes have been placed or intramuscular injections have occurred because the muscle tissue is damaged. There are two types of biopsy: open biopsy and punch biopsy. Open tissue sampling is the standard procedure. The local anesthetic is not injected into the directly affected tissue, but into the adjacent skin structures. A small incision is then made to expose the affected muscle. A tissue sample is taken from this and the wound is closed by suturing after hemostasis. Punch biopsy removes tissue using a biopsy needle that is inserted percutaneously (under the skin) into the muscle. This tissue sampling is less invasive than the open method, but only a very small sample can be obtained. If connective tissue disease of the vessels is suspected, areas of the surrounding skin, fascia, and subcutaneous adipose tissue are obtained in addition to the muscle. Further processing of the obtained biopsy specimen takes place in a pathological institute. Preferably, a muscle bundle 2 to 3 centimeters long and 0.3 to 0.5 centimeters thick is attached in situ (in situ) at two ends to a rod (sterile cotton swab) in the direction of the course of the muscle fibers to preserve the orientation of the tissue fibers, excised from the rod, and immediately fixed. A buffered six percent glutaraldehyde solution consisting of 20 to 30 millimeters with phosphate buffer is suitable as a means of fixation for electron microscopic examination and the semi-thin section method.A similar paraffin-embedded preparation fixed in a four percent formaldehyde solution is suitable for light microscopic examination. An approximately 1 x 0.5 x 0.5 cm section of muscle is then excised for immunohistochemical, enzyme histochemical, and molecular biological examination. This piece is not to be fixed or tied to a rod, but must be immediately frozen in liquid nitrogen or immediately transferred to pathology in a closed container with a moist cloth to prevent desiccation. The pathologists take over the processing and perform the histological examination. Due to limited shelf life, shipment is by courier. The glutaraldehyde- and formalin-fixed specimens are sent separately from the frozen muscle section. The containers with the muscle sections placed in the fixation solutions are attached to the outside of the Styrofoam box using adhesive tape. If they are in close proximity to the dry ice, the solutions will freeze and serious artifacts will result. Tissue removal is induced in the following conditions:
- Inflammation of the muscles (polymyositis, inclusion body myositis).
- Systemic inflammatory diseases (vasculitides, eosinophilic syndromes).
- Muscular dystrophies (limb-girdle dystrophy, Duchenne muscular dystrophy,).
- Congenital myopathies (nemaline myopathy, central core myopathy).
- Neurogenic muscular atrophies (amyotrophic lateral sclerosis, spinal muscular atrophies).
- Myopathies associated with metabolic disorders (lipid storage myopathies).
- Mitochondrial disorders (myoclonus epilepsy with “ragged red” fibers).
- Toxicity-related myopathies (chloroquine, colchicine, statins).
- Rhabdomyolyses, muscular dystrophy (muscle wasting).
- Unclear diseases of the musculature
Routine pathological examinations are:
- Elastika van Gieson (EvG) stain (fibrosis of endomysial connective tissue in myopathies).
- Modified Gömöri trichrome stain (inclusion bodies in nemaline myopathy).
- Oil red staining (lipid deposition in carnitine palmitoyl transferase deficiency).
- Acid phosphatase reaction (increased macrophage activity in inflammatory myopathies).
- ATPase reaction at different pH values (different fiber types and their impaired distribution in chronic neurogenic injury).
- NADH reaction (representation of oxidative intermyofibrillar network and its disturbances in multicore myopathy, central core myopathy).
- PAS staining (increased glycogen storage in McArdle disease).
Risks, side effects, and hazards
Rare complications include infection and wound healing disorders. Because skeletal muscle tissue is maximally irritable and susceptible to artifact, there is a risk of bruising or further injury to the tissue. Bruising, discomfort, and minor bleeding at the donor site are possible. Prior to the procedure, the physician will inform the patient of individual risks and ask about contraindications, such as allergies to the anesthetics used. Bleeding disorders, aspirin, and anticoagulants (medications used to thin the blood) are important contraindications that may allow the procedure to be performed only if the patient discontinues the medications. To ensure that the patient is physically fit for the procedure, the physician performs a physical examination in addition to taking a medical history. After the procedure, the patient can quickly resume his usual daily routine, there are only minor restrictions. He must keep the incision site sterile and dry and must not put too much stress on the affected muscle tissue.
Typical and common muscle disorders
- Muscle fiber tear
- Muscle weakness
- Compartment syndrome
- Muscle inflammation (myositis)
- Muscular atrophy (muscular dystrophy)
