Muscle biopsy
Biopsy a clinically weak muscle (MRC grade 4/5).
Biopsy is taken from the belly of the muscle, and it is important to avoid the region of the tendon.
Each specimen should be about 1-2 cm in length and 0.5 cm in width.
The specimen should be wrapped in slightly moist gauze and placed in separate labeled sterile containers until they reach the laboratory. It is important not to place the specimens in a container of saline else this will lead to artifact. Nor should the entire specimen be placed in fixative else the important histochemistry stains, protein/enzyme analysis, and mutation analysis cannot be performed.
Obtain at least two separate specimens as muscle disorders can be multifocal (e.g., inflammatory myopathies).
Freeze the specimen in isopentane cooled in liquid nitrogen. The frozen tissue is then sectioned and stained for routine histochemistry.
A separate piece of muscle is fixed in formalin or Bouin's fluid for paraffin sections.
Another piece of muscle is taken for ultrastructural examination by EM. This small piece of muscle tissue is secured on a clamp or stretched out by suturing the muscle over a tongue blade, in order to prevent hypercontraction artifact. The tissue is fixed in glutaraldehyde for plastic (resin) embedding for EM.
GENERAL MORPHOLOGIC FEATURES
Myofiber size: variable
Angulated fibers: present
Fiber groups: absent
Perifascicular atrophy: absent
Myofiber types (ATPase pH4.3, 4.6 and 9.4): Equal populations of both fiber
types; normal sized and atrophic fibers of both types
Blood vessels: normal
Amyloid (Congo red): absent
MYOPATHIC FEATURES
Necrotic fibers (Gomori trichrome, nonspecific esterase, CD68): present
De-/Regenerating fibers: present
Internal nuclei: present
Endomysial fibrosis (Masson Trichrome): mild
Fatty metaplasia: present
INFLAMMATION (CD3, CD20)
Perivascular: absent
Endomysial: absent
Vasculitis: absent
CYTOARCHITECTURAL FEATURES
Vacuoles (Gomori trichrome): absent
Target/Targetoid fibers (NADH-TR): absent
Small dark angulated fibers (NADH-TR): present
Lobulated Fibers (NADH-TR): absent
Cores (NADH-TR): absent
Minicores (NADH-TR): absent
Subsarcolemmal deposits: absent
Ragged Red Fibers (Gomori trichrome): absent
Nemaline Rods (Gomori trichrome): absent
Tubular Aggregates (Gomori trichrome): absent
COX-negative fibers (COX-SDH): within normal limits
Subsarcolemmal nuclear clusters: present
IMMUNOHISTOCHEMISTRY
MHC Class I (B1): Increased sarcolemmal staining in necrotic fibers
CD3 (A2): virtually absent
CD20 (A2): virtually absent
CD163 (A2): macrophages in endomysium and myophagocytosis
GROSS DESCRIPTION
A through C. Muscle, quadriceps, left, biopsy:
CONTAINER LABEL: Left quadriceps - fresh muscle biopsy for protocol.
RECEIVED: Unfixed on a saline soaked Telfa pad.
PIECES: 1. SIZE: 1.7 x 1.4 x 1 cm. PROCEDURE: (A) Sections are taken for
routine processing and paraffin-embedding; (B and C) samples are snap frozen
for histochemistry and placed in glutaraldehyde for possible electron
microscopy/Epon embedding; one piece is retained for frozen storage.
CASSETTES/PARTS: A1: Paraffin-embedded block; B1: Snap frozen block; C1-6:
Epon-embedded blocks, NS.
lmb/11/17/2023
Candi Bennett
MICROSCOPIC DESCRIPTION
STAINS
Paraffin sections (tissue block A1): Hematoxylin and eosin, Masson trichrome,
Congo red, CD163 (scavenger receptor cysteine-rich [SRCR] 1), CD3 (T cell
marker), CD20 (L26, B cell marker)
Cryosections (tissue block B1): Hematoxylin and eosin, Gomori trichrome,
alkaline phosphatase, nonspecific esterase, NADH-tetrazolium reductase,
succinate dehydrogenase, cytochrome oxidase-succinate dehydrogenase, ATPase
(pH4.3, 4.6 and 9.4), MHC Class I
Plastic-embedded sections (tissue blocks C1-6): Paragon
TISSUE QUALITY: Within normal limits
GENERAL MORPHOLOGIC FEATURES
Myofiber size: Mild variation
Angulated fibers: Rare
Fiber groups: Absent
Perifascicular atrophy: Absent
Myofiber types (ATPase pH4.3, 4.6 and 9.4): Equal populations of both fiber
types; normal sized and atrophic fibers of both types
Blood vessels: Within normal limits
Endomysium: Mild increase in collagen
Amyloid (Congo red): Absent, including sarcoplasmic compartment
MYOPATHIC FEATURES
Necrotic fibers (Gomori trichrome, nonspecific esterase, CD163): Present
(myophagocytosis)
De-/Regenerating fibers: Present
Internal nuclei: Present
Endomysial fibrosis (Masson trichrome): Mild
Fatty metaplasia: Mild
INFLAMMATION (CD3, CD20)
Perivascular: Sparse
Endomysial: Sparse
Vasculitis: None identified
CYTOARCHITECTURAL FEATURES
Red-rimmed vacuoles (Gomori trichrome): Absent
Vacuoles (H&E): Present (not a specific finding)
Target/Targetoid fibers (NADH-TR): Absent
Small dark angulated fibers (NADH-TR): Very rare
Lobulated Fibers (NADH-TR): Absent
Cores (NADH-TR): Absent
Minicores (NADH-TR): Absent
Subsarcolemmal deposits: Absent
Ragged Red Fibers (Gomori trichrome): Absent
Nemaline Rods (Gomori trichrome): Absent
Tubular Aggregates (Gomori trichrome): Absent
COX-negative fibers (COX-SDH): NOT increased
Subsarcolemmal nuclear clusters: Absent
Other: Not applicable
IMMUNOHISTOCHEMISTRY
MHC Class I (B1): Increased sarcolemmal labeling (patchy), labeling of
inflammatory cells and perimysium
CD3 (A1): Scattered peri- and endomysial T cells predominantly in a
perivascular distribution
CD20 (A1): NO significant B cell infiltrate is seen in this stain
CD163 (A1): highlights macrophages as part of the perivascular infiltrate and
foci of myophagocytosis
PARAGON-STAINED SECTIONS
NO further pathologic features are recognized in plastic-embedded and
Paragon-stained sections
Appropriate controls are reviewed and found satisfactory