Muscle and nerve consultation

Mayo Clinic Laboratories’ muscle and nerve consultation, in conjunction with clinical assessment and other laboratory testing, can be crucial for the diagnosis of certain neuromuscular disorders. Our neuromuscular pathologists are available to discuss muscle and nerve biopsy findings with referring clinicians. As practicing clinicians, our pathologists can also evaluate the patient, if desired.

Key testing

• MBX | Muscle Pathology Consultation
  • A muscle biopsy is essential for the diagnosis of most acquired muscle diseases and some inherited muscle diseases and can help resolve the meaning of variants of unknown significance (VUS).
  • Our pathology experts review more than 1,000 muscle biopsies annually and provide unique expertise that extends beyond muscle pathology for all muscle diseases.
  • Extensive morphological and histochemical studies are performed routinely on every frozen muscle sample.
  • Pathology reviews correlate muscle biopsy findings with clinical history, electromyography (EMG), antibody, and genetic findings. Additional histochemical and immunohistochemical studies are performed, if needed, to investigate the patient’s disease.
    • Detection of specific findings triggers further investigations to provide patients with a more definite diagnosis. For example, the detection of amyloid, routinely searched in muscle specimens, automatically triggers amyloid subtyping by mass spectrometry analysis in our Hemopathology Laboratory.
    • Features of mitochondrial myopathy in the proper clinical context can be followed (if desired by the referring physician) by mitochondrial genetic testing in muscle tissue through our Genetics and Genomics Laboratory.
• PNBX | Peripheral Nerve Pathology Consultation
  • All nerve biopsy samples are initially divided into three specimens: teased fibers, paraffin, and epoxy sections.  
    • Nerve biopsy samples are divided into multiple sections, and individual fibers are teased further.
    • Teased fiber preparations are the best way to identify pathology along the length of the nerve, such as axonal degeneration or segmental demyelination.
  • Mayo Clinic provides specimen kits with instructions for specimen collection and fixation.
  • High-quality evaluations of paraffin-embedded sections are prepared and reviewed for interstitial abnormalities, including immunohistochemistry.
  • Detailed, labor-intensive teased fiber preparations enable systemic, longitudinal assessment of nerve pathology.
    • These processes ensure appropriate diagnosis, compared to less precise processes that result in over-diagnosis of certain conditions, such as segmental demyelination.
• SPBX | Epidermal Nerve Fiber Density Consultation, Varies
  • Epidermal nerve fiber counts are prepared on cryopreserved skin preparations of 3 mm punch biopsies.
  • Standard sites for epidermal nerve fiber densities include dorsal foot, distal leg, mid-thigh, and lower abdomen.
  • Multiple sections are counted and compared to age- and sex-matched controls.
  • Paraffin sections for H&E and Congo Red are prepared for each site.
  • Counts are determined to provide evidence for small fiber neuropathy.
  • Mayo Clinic's preparations result in fewer artifacts and less frequent diagnoses of small fiber neuropathy.
    • Not all pain syndromes are due to small fiber neuropathy, and it is helpful to correctly diagnose small fiber neuropathy versus other pain causes.