david lacomis, md diseases of muscle: histopathologic features
TRANSCRIPT
David Lacomis, MD
Diseases of Muscle:
Histopathologic Features
Organization of Skeletal Muscle Including Connective Tissue (CT) Compartments
EPIMYSIUM•Loose CT•Blood vessels
PERIMYSIUM•Septa•Nerve branches•Muscle spindles•Fat•Blood vessels
ENDOMYSIUM•Muscle fibers•Capillaries•Small nerve fibers
Perimysialconnective tissue
Endomysialconnective tissue
Normal H&E-Stained Frozen Cross-Section of Skeletal Muscle
Note uniform sizes, polygonal shapes, and eccentric nuclei.
Normal H&E-Stained Longitudinal Paraffin Section
Note the banding pattern. Nuclei are eccentrically placed.
Spindle
Nerve Twig
Normal Structures: Muscle Spindleand Associated Nerve Fibers (Gomori trichrome)
Can be identified by the esterase reaction due to the presence of acetylcholinesterase.
Neuromuscular Junctions
Neuromuscular Junction (Electron Microscopy)
postsynaptic
presynaptic
Histochemical Staining Intensity Based on Fiber Types
Type I Type II Type IIB
Slow twitch, oxidative; stain dark with Gomori trichrome, NADH, SDH, and ATPase at acidic pH; more lipid than type II
Fast twitch, glycolytic; stain dark with ATPase at alkaline pH and with PAS stains, as well as phosphorylase
Intermediate staining intensity with ATPase pH4.6
NADH = nicotinamide adenine dinucleotideSDH = succinic dehydrogenaseATPase = adenosine triphosphatase
Type I fibers are light Type II fibers are dark (pattern reverses at ATPase pH 4.3)
Normal (ATPase pH 9.4)
Ultrastructure of a Sarcomere*
*Extends from Z-band to Z-band. A band includes overlap of actin and myosin. Note arrangement of thick and thin filaments.
Z ZM
H band
ActinMyosin I bandI band
A band
Dark A-bands
Light I-bands
Z-band is present in the middle of the light band
Thin filaments are attached at the Z-band
Normal (Electron Microscopy)
Classification of Myopathies
ACQUIRED INHERITED
Inflammatory Myopathies Dystrophies
Polymyositis (PM) Dystrophinopathies
Dermatomyositis (DM) Limb-Girdle
Inclusion body myositis (IBM) Myotonic
Granulomatous myositis Facioscapulohumeral (FSHD)
Infectious myositis Oculopharyngeal (OPD)
Toxic Distal
Endocrine Congenital
Metabolic
Mitochondrial
Glycogen & lipid storage
Muscle Biopsy
Often necessary for final diagnosis of myopathy Choose site based on clinical, electrodiagnostic, or
imaging features Avoid “end-stage” fatty muscle
Frozen sections most useful Routine stains Histochemistry Immunohistochemistry
Polymyositis(Longitudinal Paraffin-Embedded Section)
In all myopathies, degenerating fibers stain pale initially and then become digested by macrophages.
Mononuclear inflammatory cell infiltrates and many basophilic regenerating fibers (arrow)
Polymyositis(Longitudinal Paraffin-Embedded Section-Higher Power)
Regenerating fiber (non-specific) Fiber is basophilic due to presence of increased RNA
and DNA. Activated plump nuclei and prominent nucleoli
As regeneration advances, a myotube “bridge” is formed.
Polymyositis(Longitudinal Paraffin-Embedded Section-Higher Power)
Invasion of a Non-necrotic Fiber by Inflammatory Cells
Seen in polymyositis, inclusion body myositis, and a few dystrophies.
Myophagocytosis(Esterase Stain)
Macrophages are ingesting the remnants of a degenerating fiber. This is a non-specific myopathic finding.
Dermatomyositis
Perifascicular atrophy & Degeneration Perimysial nflammatory cells surround a blood vessel. Inflammatory cells tend to be B-cells. Vasculitis with bowel infarction and subcutaneous
calcifications sometimes occur in the childhood form.
Perifascicular Atrophy(NADH-Reacted Section)
MAC is the terminal component of the complement pathway. It is often deposited in capillaries in dermatomyositis.
Membrane Attack Complex (MAC)(Immunohistochemical Stain)
Features of chronic myopathy with endomysial inflammation and rimmed vacuoles are characteristic.
Inclusion Body Myositis (IBM)
Vacuole
Invaded fiber
Lymphocytic inflammation
“Rimmed vacuoles”
IBM: Vacuoles contain amyloid.
(Congo Red)
IBM Intracytoplasmic (within Vacuoles) or Intranuclear Filamentous Inclusions
Giant cell
Granulomas tend not to cause significant damage to adjacent myofibers.
Granulomatous Myositisin a Patient with Sarcoidosis
Characteristic of most endocrine myopathies and steroid myopathy
Endocrine Disturbance Type II Fiber Atrophy(ATPase pH9.4)
Inherited PolyneuropathyChronic Neurogenic Atrophy
Groups of angulated atrophic fibers Marked variation in myofiber size
Acute Denervation(NADH Reaction)
Manifested by small, darkly staining angulated fibers.
Denervated fibers also stain darkly with non-specific esterase.
Denervation(Esterase Stain)
Target fibers noted. Light center surrounded by a darker rim. Generally only seen in type I fibers.
Chronic Neurogenic Processes(NADH Reaction)
Fiber type grouping
Chronic Neurogenic Atrophy(ATPase Reaction)
Opaque or hyaline fibers (arrows) Increase in endomysial connective tissue
Frozen Section from a Patient withDuchenne Muscular Dystrophy
Group of basophilic regenerating fibers
Normal Immunohistochemical Stain for Dystrophin(Subsarcolemmal Staining)
Duchenne Muscular Dystrophy (Absent Staining for Dystrophin)
split fiber(non-specific chronic change)
Becker Muscular Dystrophy (Reduced but Present Staining)
Female Carrier of Duchenne Muscular Dystrophy
(A Mosaic Staining Pattern)
INHERITANCE GENETICABNORMALITY
DISORDER
X-linked DystrophinEmerin
Duchenne, Becker MDEmery-Dreifuss MD
AD MyotilinLamin A/CCaveolin – 3PABP2-crystallin/Desmin
Limb-Girdle MD (LGMD 1A)LGMD 1BLGMD 1COculopharyngealMyofibrillar Myopathy
AR Calpain – 3Dysferlin Sarcoglycana Sarcoglycan SarcoglycanΔ SarcoglycanTelethonin
LGMD 2ALGMD 2BLGMD 2CLGMD 2DLGMD 2ELGMD 2FLGMD 2G
Mutations in “Limb-Girdle” and Other Dystrophies
Sarcolemma
nucleus
Lamin A/C(emerin)
sarcoglycans
Dystroglycancomplex
Laminin-2
Extracellular Matrix
Dysferlin
Caveolin 3
Actin
Dystrophin
Locations of Affected Proteinsin Muscular Dystrophies
Emery-Dreifuss Muscular Dystrophy(Gomori Trichrome-Stained Frozen Section)
Necrotic fiber
Variation in fiber size with many hypertrophic fibers Increase in endomysial connective tissue Nonspecific so-called dystrophic changes seen in many of
the muscular dystrophies. Can also be seen in any chronic myopathic disorder. This disorder is due to loss of the protein emerin.
Myotonic Dystrophy
Chronic changes Marked excess in internalized nuclei Variation in fiber sizes Nuclear clumps (not shown)
(H & E, Paraffin)
The excess of internalized nuclei can lead to nuclear chains.
Myotonic Dystrophy(NADH-Reacted Section)
Ring fibers in which myofilaments are organized in different directions
Fascioscapulohumeral Dystrophy (FSHD)
The majority of dystrophies do not have a specific histopathologic appearance.
Clinical features are also very important. For example, winging of the scapula is
characteristic of FSHD.
FSH Dystrophy
Variable non-specific changes Range from scattered atrophy to
“dystrophic” features. Inflammation can be present (arrow).
Central areas of absent staining in the dark type I fibers Mitochondria absent
Congenital Myopathies: Central Core Myopathy(NADH)
Congenital Myopathies: Central Core Myopathy(NADH)
The core consists of disorganized myofibrils and the area is devoid of mitochondria.
Congenital Fiber Type Disproportion(H&E)
Bimodal size population
Smaller fibers are type I More numerous Stain lightly
Larger or normal fibers are type II
Congenital Fiber Type Disproportion(ATPase pH 4.3)
Eosinophilic inclusions present.
Nemaline Myopathy
Eosinophilic inclusions stain darkly.
Nemaline Myopathy(Gomori Trichrome)
Named for thread-like appearance Inclusions extend from Z-band to Z-band
Nemaline Myopathy(Electron Microscopy)
Muscle Biopsy from an Infant
Internalized nuclei predominant. Consistent with centronuclear myopathy. Can be seen in other disorders such as
myotonic dystrophy with congenital onset.
Muscle Biopsy from an Infant:Centronuclear Myopathy
Central position of the nucleus resembling an embryonic myotube
Metabolic: Inherited – Mitochondrial Myopathy
Ragged red fiber present (Gomori trichrome) Due to proliferation of abnormal mitochondria
SDH-rich fibers are seen with mitochondrial proliferation. SDH is a respiratory chain enzyme encoded by nuclear DNA.
Mitochondrial Myopathy(Succinic Dehydrogenase Reaction)
Cytochrome Oxidase (COX) Respiratory Chain EnzymeNormal Fibers
Many COX-Negative Fibers
COX-negative fibers are usually seen with mtDNA mutations.
Aggregates of mitochondria containing paracrystalline inclusions are frequent.
Non-specific
Mitochondrial Disorders(Electron Microscopy)
Mitochondrial Disorders(Electron Microscopy)
Higher power view of paracrystalline inclusion
Increased lipid storage Seen in carnitine deficiency states (primary or secondary) Sometimes as a consequence of certain toxins Focal increases can be non-specific.
(Oil-Red-O Stain)
Lipid Storage Myopathy(Electron Microscopy)
Some glycogen storage myopathies, such as myophosphorylase deficiency (McArdle’s Disease), cause subsarcolemmal blebs.
PAS-positive due to the presence of glycogen. Only with acid maltase deficiency is glycogen
deposited in lysomsomes.
Glycogen Storage Myopathies
Subsarcolemmal collection of glycogen is shown.
McArdle’s Disease(Electron Microscopy)
Acid Maltase Deficiency(Acid Phosphatase)
Due to the intralysosomal activity of this enzyme
Prominent staining with acid phosphatase in vacuoles
Vacuolar myopathy noted.
Normal Glycogen(PAS Stain) Control
Increased Glycogen
Acid maltase deficiency Increased glycogen (diffusely and in vacuoles)