Neuromuscular

NEMALINE RODS
General
  Description
  Characteristics
    Clinical
    Pathology
Infant
  Diffuse
  Type 1 small
  Ultrastructure
  Congenital
Child
  ACTA1
Adult
  RYR3
  SLONM
DDx
Atypical

Z-Disk streaming

Nemaline Rod: Muscle Pathology
  • Light microscopy
    • Rods best visualized with
      • Gomori trichrome stain
      • Toluidine blue stained plastic sections
      • Phalloidin
    • Dark blue structures
    • Most in muscle fiber cytoplasm
      • Often in regions with disrupted sarcomere structure
  • Contain
    • Z-line like material
    • α-actinin, actin & tropomyosin ± desmin at the periphery
  • Rods: Occur in
    • Congenital myopathies
      • TPM3: Rods, Preferentially in type 1 fibers; Type 1 fiber predominance
      • ACTA1: Rods, Numerous, Most in small fibers, Cytoplasmic & Nuclear; Clusters of glycogen & actin filaments
      • TNNT1: Rods, Central in muscle fibers; Type 1 fibers small
      • KBTBD13: Rods, Diffusely distributed, All fibers; Type 1 fibers Predominant & Large
      • KLHL40: Rods, Many small; No normal myofibers
      • LMOD3: Rods Surrounded by "thin filament fringe"; Thickened Z disks
      • NEB: Normal & Small size fibers; Globular in severe disease; Desmin cytoplasmic aggregates
    • Patterns
    • Adult onset: SLONM
  • Similar staining: Cytoplasmic bodies
    • Rods & Cytoplasmic bodies: Mainly visible on Gomori trichrome & Toluidine blue
    • Cytoplasmic bodies: Have a surrounding halo; Round shape; Large size
    • Rods: No halo; More per each individual fiber; Higher frequency of involved fibers
  • Also see: Rods or Cytoplasmic bodies in target fibers

Nemaline rod myopathy: Infantile

 
Gomori trichrome
Nemaline rods in gastrocnemius muscle from 4 month old child


No nemaline rods in quadriceps muscle from same child biopsied at 2 months of age

Nemaline rod myopathy, Infantile: Toluidine blue stains

Nemaline rod myopathy, Infantile: Other stains


H&E stain
Muscle fiber sizes: Varied

H&E stain

H& E stain
Muscle fiber size: Varied
Refractile rods can be seen
ATPase stain, pH 9.4
Type I muscle fiber predominance

H& E stain

Rods: Actin stain


Phalloidin staining for actin
Focal (bright green), large and small aggregates of actin are present in some muscle fibers

Phalloidin staining for actin


Nemaline Rod Ultrastructure
Infantile-onset Rod myopathy

From: R Schmidt
 

Nemaline Rods

  • Electron dense
  • Sizes: Length 1-7 μm; Width 0.3-2 μm
  • Long axis: Parallel to muscle fiber
  • Longitudinal section: Striations parallel & perpendicular to long axis
  • Transverse section: Lattice structure like Z disk
  • Thin filaments: In continuity with rods

From: R Schmidt
From: R Schmidt
Nemaline Rods: Mouse Model

From E Hardeman
Electron microscopy of rods from Z-lines in Met9Arg αTMslow mouse

Nemaline rod myopathy, infant (8 months of age): Type 1 muscle fiber smallness

Rods: More prominent in smaller muscle fibers

Gomori trichrome

ATPase pH 9.4
Type 1 muscle fibers: Small (Pale)

H&E
Muscle fiber sizes: Bimodal

NADH
Internal architecture of muscle fibers: Irregular

Rod Myopathy: Congenital + Arthrogryposis


H&E stain
Fiber sizes: Bimodal distribution

Gomori trichrome stain
Rods
  Dark-stained: Punctate or Clustered regions, Often sub-sarcolemmal
  More common in smaller muscle fibers

Gomori trichrome stain

Gomori trichrome stain

ATPase pH 9.4 stain
Fiber types
  Type 1 fibers: Usually small
  Type 2 fibers: Larger; Abnormal intermediate staining (2C) at ATPase pH 4.3

ATPase pH 4.3 stain

NADH stain
Rods: In clusters in muscle fibers

Toluidine blue stain

Toluidine blue stain

Nemaline rod myopathy, Childhood: 2 Different patterns

Rods: In smaller muscle fibers

GT stain
 
ATPase stain, pH 9.4
Type I muscle fibers: Smaller than type II
Rods: In small & large muscle fibers

GT stain
Type I predominance

ATPase stain, pH 9.4
Fiber size variation: Bimodal distribution

H&E stain

Rods: Adult nemaline myopathy
  Several patterns

Rods: Larger & Aggregated
 
Gomori trichrome
Rods: May cluster near myonuclei (Arrow)

Gomori trichrome
Rods: Small & Diffusely distributed in some muscle fibers
  Myopathic features: Varied muscle fiber size; Internal nuclei; Endomysial connective tissue increased

Gomori trichrome
Gomori trichrome

Gomori trichrome

Gomori trichrome

H&E stain

Rods: Atypical


Gomori trichrome stain
Rod-like Aggregates
  Stain dark on Gomori trichrome
  Near myotendinous junctions

Gomori trichrome stain


Toluidine blue stain
Rod-like Aggregates: Rod shape in fixed sections
Rod-like Aggregates (Ultrastructure)
  Dark stained
  Internal structure: Amorphous
  Shape: Irregular; Polygonal
  Halo: Contains linear structures

Rods: ACTA1 mutation (M46T)

13 yo male with Rod myopathy
No rods in muscle biopsy of same patient at 1 year old

H&E stain
Fiber Sizes
  Small
  Mild variation
Myonuclei
  Mildly large
  Shapes: Irregular

H&E stain

Congo red stain
Rod Myopathy (ACTA1): Myonuclei
  Abundant
  Shapes: Irregular
  Sizes: Large

Congo red stain

ATPase pH 4.3 stain
Type I muscle fiber predominance

Gomori trichrome stain
Rods
  Irregular shaped clusters of dark stained material in myofiber cytoplasm

Gomori trichrome stain

Gomori trichrome stain

Phalloidin stain for Actin
Actin aggregates in Rod myopathy (Arrows)
  Clustered in regions of muscle fiber cytoplasm

Phalloidin stain for Actin

Toluidine blue stain

Toluidine blue stain
Rods
  Morphology: Dark-stained rod-shaped inclusions
  Distribution: Clustered or scattered in myofiber cytoplasm

Toluidine blue stain

Toluidine blue stain
Rods
  Dark-stained rod-shaped inclusions: Often aligned along Z-bands
Rods
  Rods occuring in a subsarcolemmal cluster
Nemaline Rods
  Electron dense
  Sizes: Length 1-7 μm; Width 0.3-2 μm
  Long axis: Parallel to muscle fiber
  Longitudinal section: Striations parallel & perpendicular to long axis
  Transverse sections: Lattice structure like Z disk
  Thin filaments: May be in continuity with rods
Rod Myopathy: Same patient as above at 1 year old
  No rods
  Type 1 muscle fibers: Small

H&E stain
Mucle fiber sizes: Varied

Gomori trichrome stain
No rods are visible on Gomori trichrome stain

Gomori trichrome stain

Congo red stain
Nuclear shapes: Irregular
Mucle fiber sizes: Varied

NADH stain

ATPase pH 9.4 stain
Type I muscle fibers: Small

ATPase pH 4.3 stain

Z-Disk: Streaming & Other disorders
Z-Disk: Streaming
Z-disk Streaming
  Crosses up to 2 sarcomeres
Return to Rod myopathies

References
1. J Neuropathol Exp Neurol 2022;81:304-307

10/26/2022