Inherited Diseases of Muscle: Histologic Features David Lacomis, MD

Classification of Myopathies ACQUIREDINHERITED Inflammatory Myopathies Dystrophies  Polymositis (PM)  Dystrophinopathies  Dermatomyositis (DM)  Limb-Girdle  Inclusion body myositis (IBM)  Myotonic  Granulomatous myositis  Facioscapulohumeral (FSHD)  Infectious myositis  Oculopharyngeal (OPD) Toxic  Distal EndocrineCongenital Metabolic  Mitochondrial  Glycogen & lipid storage

 Opaque or hyaline fibers  Increase in endomysial connective tissue Frozen Section from a Patient with Duchenne 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 GENETIC ABNORMALITY DISORDER X-linkedDystrophin Emerin Duchenne, Becker MD Emery-Dreifuss MD ADMyotilin Lamin A/C Caveolin – 3 PABP2  -crystallin/Desmin Limb-Girdle MD (LGMD 1A) LGMD 1B LGMD 1C Oculopharyngeal Myofibrillar Myopathy ARCalpain – 3 Dysferlin  Sarcoglycan a Sarcoglycan  Sarcoglycan Δ Sarcoglycan Telethonin Fukuitin-rel prot LGMD 2A LGMD 2B LGMD 2C LGMD 2D LGMD 2E LGMD 2F LGMD 2G LGMD 2H LGMD 2I Mutations in “Limb-Girdle” & Other Dystrophies

Sarcolemma nucleus Lamin A/C (emerin) sarcoglycans    Dystroglycan complex Laminin-2 Extracellular Matrix Dysferlin Caveolin 3 Actin Dystrophin    Locations of Affected Proteins in 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.

 Basophilic subsarcolemmal structures are sarcoplasmic masses.  Sometimes occur in chronic myopathies such as FSH and myotonic dystrophy.

Sarcoplasmic Masses Stained darkly with NADH reaction

Oculopharyngeal Muscular Dystrophy (OPD)  Variation in muscle fiber size with atrophic angulated fibers  Sometimes contain rimmed vacuoles

Higher power view of Gomori trichrome-stained section  Angulated fibers  Fiber containing a large rimmed vacuole

Oculopharyngeal Dystrophy Gomori trichrome  Ragged red fibers are sometimes seen.  Characteristic of proliferation of abnormal mitochondria.

 May be identified by electron microscopy in OPD Intranuclear Filamentous Inclusions

 Central areas of absent staining in the dark type I fibers  Mitochondria absent 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 MELAS Syndrome  Ragged red fiber present

 SDH-rich fibers are seen with mitochondrial proliferation MELAS Syndrome Succinic dehydrogenase reaction

“Ragged-red” Fibers H&E

SDH-rich Fibers

Cox Normal 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

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. Glycogen Storage Myopathies

McArdles Disease: Phosphorylase Reaction Normal Control Disease (Absent)

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)

 Glycogen is digested by diastase in most glycogen storage diseases.

Aggregates of Glycogen within Autophagic Vacuoles (Acid Maltase Deficiency) Electron microscopy

 Tubular aggregates occur in an inherited myopathy, non- specifically, and in some patients with myalgias. Miscellaneous Disorder

Bright red with Gomori trichrome

Stain darkly with NADH, no staining with SDH Miscellaneous Disorder

Tubular Aggregates Via Electron Microscopy