JPC SYSTEMIC PATHOLOGY

NERVOUS SYSTEM

January 2020

N-M21 (NP)

 

SIGNALMENT (JPC #2013034):  Military working dog, age unspecified.

 

HISTORY:  Incidental finding

 

HISTOPATHOLOGIC DESCRIPTION:  Brain, cerebellum and brainstem:  Diffusely in the cerebellar molecular layer there are moderate numbers of 10-20 µm diameter, round to oblong, often-bulbous structures with a blue-gray, finely granular core surrounded by a 2-4 µm wide light amphophilic, finely granular zone and further outlined by a 1 µm thin zone of eosinophilic material (peripheralized axoplasm).  Moderate numbers of neurons in the brainstem contain intracytoplasmic, often perinuclear, yellow-gold pigment (lipofuscin).

 

MORPHOLOGIC DIAGNOSIS:  Brain, cerebellum, molecular layer: Polyglucosan bodies, numerous, breed unspecified, canine.

 

CONDITION: Incidental Lafora-like bodies

 

SYNONYMS:  Lafora bodies; neuronal glycoproteinosis

 

GENERAL DISCUSSION:

·      Intracytoplasmic inclusions composed of complex glycoprotein polymers (polyglucosan bodies) are called Lafora bodies, Lafora-like bodies, corpora amylacia, or amylopectin bodies

·      Corpora amylacea: term used when associated with aging (usually >8 years old); located in astrocytes and axons, not in perikaryon; also found in normal aging cells in most tissues

·      Incidental Lafora bodies:  most common form; intracytoplasmic within neurons and neuronal processes and free in neuropil

·      Lafora bodies associated with Lafora disease (Lafora-like disease):  Rare; Lafora bodies occur in high numbers through the brain, intracytoplasmic within neuron soma, dendrites, and less frequently in axons; most numerous in Purkinje cells and neurons of the caudate, thalamic, and periventricular nuclei

·      Amylopectin bodies:  a third type of polyglucosan body very similar morphologically to Lafora bodies and corpora amylacea, but found in tissues of patients with glycogen storage disease type IV or glycogen branching enzyme deficiency

·      Lafora-like disease of dogs:

·      Affected breeds include: Basset hounds, beagles, poodles, and high incidence among miniature wirehaired dachshunds

·      A study indicated that 50% of a study cohort of miniature wirehaired dachshunds carried at least one copy of the EPM2B mutation responsible for Lafora’s-like disease (Sainsbury, Vet Rec. 2014)

 

PATHOGENESIS:

Lafora-like disease of dogs:

·      Disease is due to a repeat expansion (triplet repeat disorder) of the EPM2B gene that encodes malin, resulting in progressive myoclonus/epilepsy

·      The first triplet repeat disorder ever discovered in domestic animals

·      Malin is a ubiquitin ligase that normally ubiquitinates laforin for degradation and also forms a complex with laforin to ubiquinate other enzymes involved in glycogen synthesis

·      Abnormality of carbohydrate metabolism (inability to degrade laforin) > accumulation of glycogen and glycosaminoglycans > widespread, primary intraneuronal formation of polyglucosan bodies >  late stage neurologic manifestation of progressive myoclonus/epilepsy

 

TYPICAL CLINICAL FINDINGS:

·      Lafora bodies:  Often incidental finding in aged animals

·      Inherited late-onset Lafora disease: myoclonic epilepsy with progressive neurologic deterioration

·      Severity of clinical signs does not correlate with number of Lafora bodies

 

TYPICAL GROSS FINDINGS:

·      No significant gross lesions

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

·      Lafora body: 5-20 µm, homogenous, basophilic to amphophilic, non-membrane-bound, spherical inclusions with a central basophilic core and a peripheral halo of radiating filaments

·      Incidental form:  intracytoplasmic within neurons and neuronal processes and free in neuropil; found throughout the brain (cerebellar Purkinje cells and thalamic neurons) and spinal cord (caudal lumbar, sacral, and caudal segments)

·      Lafora disease form:  intracytoplasmic within neuron soma, dendrites, and less frequently in axons; reported in the hypothalamus and cerebellum

·      Other reported sites include heart, skeletal muscle, liver, apocrine sweat gland, smooth muscle layer of the urinary bladder (Chambers, Vet Pathol. 2018), as well as peripheral nerves

 

ULTRASTRUCTURAL FINDINGS:

·      Cytoplasmic accumulation of non-membrane-bound admixture of 9nm diameter interwoven filaments, electron-dense bodies, and glycogen

·      Appears to be associated with rough endoplasmic reticulum and Golgi

 

ADDITIONAL DIAGNOSTIC TESTS:

Lafora bodies:

·      Histochemistry, positive staining:  strongly PAS positive (diastase resisitant), Alcian blue, Best’s carmine, methenamine silver, Weil’s

·      With toluidine blue, Lafora bodies exhibit lower alcohol-resistant metachromasia than corpora amylacia

·      Negative staining:  stains for glycogen, lipids, minerals, and nucleic acid

·      Immunohistochemistry: immunoreactive for calbindin, laforin, hsp70, alpha/beta synuclein, ubiquitin, LC3, p62

Corpora amylacea:

·      Immunohistochemistry:  immunoreactive for both human PGBs and neurofilaments suggesting a mixed neuronal-glial origin

 

DIFFERENTIAL DIAGNOSIS:

·      Polyglucosan bodies have to be discriminated from Buscaino bodies (post mortem artifact), edema, or storage disorders

·      Amylopectin bodies:  A third type of polyglucosan body very similar morphologically to Lafora bodies and corpora amylacea, but found in tissues of patients with glycogen storage disease type IV or glycogen branching enzyme deficiency

 

COMPARATIVE PATHOLOGY:

·      Canine Lafora disease is similar to human Lafora disease:  in humans, due to mutation (although not a repeat expansion mutation) in either the EPM2A gene (encodes laforin) or the EPM2B gene (encodes malin); Lafora bodies have similar immunohistochemical properties between dogs and humans (Chambers, Vet Pathol. 2018)

·      Lafora disease occasionally reported in other species including: Feline, ox, fennec fox, cattle, Japanese red fox, gray-headed flying fox, and avian species (cockatiels, juvenile parrots, chickens and psittacines)

·      Reports of neurodegenerative diseases in birds are rare

·      Incidental Lafora bodies have been reported in a raccoon, cats, and cattle

 

References:

1.    Cantile C, Youssef S.  Nervous system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6^th ed. Philadelphia, PA: Elsevier Saunders; 2016: 255, 292.

2.    Chambers, J, Thongtharb A, Shiga Takanori, et al. Accumulation of Laforin and Other Related Proteins in Canine Lafora Disease With EPM2B Repeat Expansion. Vet Pathol. 2018; 55(4): 543-551.

3.    Frosch MP, Anthony DC, De Girolami U. The central nervous system. In: Kumar V, Abbas AK, Aster JC, eds. Robbins and Cotran Pathologic Basis of Disease. 9^th ed. Philadelphia, PA: Elsevier; 2015: 1253.

4.    Gabor LJ, et al. Polyglucosan inclusions (Lafora bodies) in a gray-headed flying fox (Pteropus poliocephalus). Jour Vet Diagn Invest. 2010; 22(2):303-304.

5.    Hamir AN. Pathology of neurologic disorders of raccoons (Procyon lotor). Jour Vet Diagn Invest. 2011; 23(5): 873-884.

6.    Honnold SP, et al. Lafora's-like disease in a fennec fox (Vulpes zerda). Jour Zoo Wildl Med. 2010; 41(3):530-534.

7.    Miller AD, Zachary JF. Nervous system. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6^th ed. St. Louis, MO: Mosby Elsevier; 2016: 952.

8.    Sainsbury R. DNA screening for Lafora's disease in miniature wire-haired dachshunds. Vet Rec. 2014; 175(22):568.

9.    Stent A, et al. Giant axonal neuropathy–like disease in an Alexandrine parrot (Psittacula eupatria). Jour Vet Diagn Invest. 2015; 27(5): 611-615.

10. Vandevelde M, Higgins RJ, Oevermann, A. Veterinary Neuropathology. Ames, IA: Wiley-Blackwell; 2012: 181-182.

11. Wohlsein P, Deschl U, Baumgartner W. Nonlesions, Unusual Cell Types, and Postmortem Artifacts in the Central Nervous System of Domestic Animals. Vet Pathol. 2012;50(1) 122-143.