Lab diagnosis and histopathology of Inflammatory Myopathies Polymyositis Dermatomyositis and Inclusion body myositis

1. Recent Concepts in
Inflammatory
Myopathies
Krushna Chandra Pani
Ipsita Panda

2. Introduction
Classification
Clinical Features
Extramuscular Features
Differential Diagnosis
Laboratory Diagnosis
Histopathology
Serology
Outline

3. Introduction
• Largest group of potentially treatable myopathies in children and adults.
• Heterogeneous group of acquired muscle diseases with distinct clinical,
pathological and histological features.
.
Elevated creatine kinase
serum activity
Inflammatory cells in
the muscle biopsy.
Subacute symmetrical proximal muscle weakness of
the limb girdle muscles (Sparing of ocular muscles)

4. Infective Autoimmune/Idiopathic
1. Viral
2. Bacterial
3. Fungal
4. Protozoal
5. Helminthic
Generalised Focal
1. Inclusion body myositis
2. Dermatomyositis (DM)
3. Polymyositis(PM)
4. Overlap syndromes
5. Necrotizing myopathy(NAM)
6. Eosinophilic myositis
7. Granulomatous myositis
1. Localized nodular myositis
2. Monomelic myositis
3. Angiopathic myositis
4. Eosinophilic myositis
5. Macrophagic myofasciitis
6. Inflammatory pseudotumor
7. Orbital myositis
Classification
Mastaglia FL. Inflammatory muscle diseases. Neurol India. 2008 Jul-Sep;56(3):263-70. Review.

5. • Sporadic disorders with an overall annual incidence of approximately one
in 100,000.1
• Bimodal age of onset 10-15 years and 45- 60 years has been reported.
• Female to male ratio is 2:1 except in inclusion-body myositis where it is
reversed.
• Prevalence of the disease is the highest in the Japanese and the lowest in
blacks.
• HLA associations include B8, DR3 and DRW52.
Epidemiology
Dimachkie MM, Barohn RJ, Amato AA. Idiopathic inflammatory myopathies. Neurol Clin. 2014
Aug;32(3):595-628, vii. doi: 10.1016/j.ncl.2014.04.007. Review

6. Clinical Features
Dermatomyositis:
• Acute to insidious progressive proximal muscle weakness
• Accompanying or preceding cutaneous manifestations.
• Affects both children(5-10yrs) and adults(40-50yrs)
• Painless weakness except patients with acute disease or subcutaneous calcifications.
• May affect bulbar muscles causing dysphagia
• Juvenile dermatomyositis:
•Misery: irritable,flushed face, fatigue and malaise
• Pain after a febrile episode and skin rash.
•Subcutaneous calcinosis of the elbows and knees with ulceration.
• Amyopathic DM( DM sine myositis) present with only the skin rash and no weakness
though muscle histology may show some inflammation.

7. Clinical Features
• Lesions are photo-sensitive and may be aggravated with exposure to UV radiation.

8. Clinical Features
Polymyositis:
• Diagnosis of exclusion: Subacute proximal myopathy in adults who DO NOT
• Have rash or other cutaneous manifestations
• Family h/o neuromuscular disease
• Exposure to myotoxic drugs: Statin (SANAM), penicillamine, zidovudine
• Involvement of facial or ocular muscles
• Any endocrinopathies
• Clinical phenotype of Inclusion body myositis.

9. Clinical Features
Inclusion Body Myositis:
Sporadic Hereditary
• Most common IIM in >50years
• Slow, relentlessly progressive course
• Quadriceps muscle more than hip flexor weakness
• Finger flexor weakness leading to loss of dexterity
• Markedly asymmetric
• Dysphagia is a significant problem as it affects 50 to 70% of patients
• Mild to moderate facial weakness is frequently demonstrated (55%)
• Congenital and childhood cases
• Mutations in GNE gene

10. Clinical Features
Necrotising Autoimmune Myositis:
• Accounting for 19% of inflammatory myopathies.
• Affects adults mostly during winters.
• May be associated with:
• Viral infections
• Connective tissue disorders like scleroderma
• After statin therapy
• Associated with neoplasms
• Cardiomyopathy or interstitial lung disease

11. Extra-muscular Features
• Pulmonary dysfunction
Interstitial lung disease: 10-25% of adult IIM
Presents with dyspnoea and cough.
• Cardiac disturbances: AV conduction defects, tachyarrythmias, dilated
cardiomyopathy
• Arthralgias and synovitis or deforming arthropathy: Subluxation in the inter-
phanagyeal joint.
Lesley Ann Saketkoo et al Curr Rheumatol Rev. Author manual 2010 May; 6(2): 108–119

12. Associated With Malignancy
• May be due to the clinical course of IM itself or due to paraneoplastic syndrome.
• Myositis specific antibodies are detected in serum of patients with IM and they are
less likely in cancer associated myopathy.
• Peak incidence of within 2 years on either side of the diagnosis of IM.
• Cancer is greater in patients with DM 27-40%, than those with PM, 15-18%.
• The prevalence of malignancy in Indian patients with IM is 7%.
Kannan MA, Sundaram C, Uppin M, Mridula R, Jabeen SA, Borgohain R. Incidence of malignancies in biopsy-proven inflammatory myopathy.
Neurol India. 2013 Mar-Apr;61(2):152-5. doi: 10.4103/0028-3886.111121. Erratum in: Neurol India. 2013 May-Jun;61(3):341

13. •Mostly NH B-cell lymphoma
• Poor prognosis
• Older and more frequently with DM
Associated With Malignancy
• DM associated ovarian cancer, breast cancer, melanoma, colon and pancreatic
cancers.
• PM is associated with lung and bladder cancers
• Gastrointestinal tract adenocarcinoma and small and non-small cell carcinoma
of the lung are common malignancies in necrotising autoimmune myopathy.

14. Overlap Syndromes
• Associated with auto-immune disorders or connective tissue.
• Mostly in association with DM.
• Systemic sclerosis and Mixed connective-tissue disease(MCTD)
• Sclerotic thickening of dermis, esophageal hypomotility, microangiopathy and
calcium deposits.
• Associated with specific Myositis Associated- antibody: Anti-PM/Scl directed
against nucleolar protein complex.

15. Differential Diagnosis

16. Diagnostic Criteria:

17. Clinical Criteria
Creatinie Kinase
Electromyography
MRI
Myositis specific
Antibodies
Histopathological
Features

18. Laboratory Diagnosis
Creatine kinase & Inflammatory Markers
• Muscle derived enzyme in serum most sensitive indicator.
• Parallel with disease activity.
• Highest in NAM and lowest in IBM.
• Normal values at rest are usually between 60 to 174 IU/L
• Elevated to more than 50 times the upper limit.
• Decrease or increase correlates with good treatment response or relapse.

19. Laboratory Diagnosis
Laboratory Test Significance
Muscle enzymes (CK MM isoenzyme
fraction, AST, ALT, LDH, aldolase)
May be normal in 5 to 10% of patients
CK MB fraction Probably arises from myoblasts rather
than from cardiac muscle
Creatinuria(>2000mg/day) Excretion of creatinine in urine
Serum Creatinine Low
Myoglobin in serum and urine May correlate with muscle inflammation
better than muscle enzymes
Erythrocyte Sedimentation rate Elevated in 50% of patients with IIM. Does
not correlate with disease activity.

20. CK MB elevation in Inf Myositis CK MB elevation In Myocardial
infarction
Ratio of CK-MB to total CK much higher
Persistent elevation of MB levels
Macro-CK type 1, a complex of a CK
isoenzyme and immunoglobulin are
elevated
Laboratory Diagnosis

21. Laboratory Diagnosis
Elevated levels of C3d
Serum IgG levels are elevated
IgE elevated in juvenile DM
Levels in plasma of von Willebrand factor VIII-related antigen
Levels of thrombomodulin, another marker of endothelial
damage in plasma
Levels of neopterin, a marker of activated mononuclear cell
responses in serum, correlate with disease activity in patients
with JDM
IMMUNOLOGIC ABNORMALITIES IN THE IIM
Antinuclear autoantibodies (ANAs) are seen in 60 to 90% of
patients with IIM

22. Electromyography:
• Myopathic motor unit potentials
• Short duration, low amplitude, polyphasic units on voluntary action
• Increased spontaneous activity with fibrillations
• Complex repetitive discharge.
• Positive sharp waves.
• Diffuse electrical myotonia is a prominent finding in SANAM
• Helpful in assessing relapsing weakness during treatment with
corticosteroids.

23. Muscle Imaging:
• Fat-suppressed and short tau inversion recovery skeletal muscle MRI
• Show fibrosis or diffuse or patchy signal symmetric increase in the
proximal muscles
• Odema of intermuscular fascia due to inflammation

24. Histological Features:
Muscle Biopsy:
Perimysium Endomysium
Latin mus (=mouse)

25. Muscle Fibre types:
• On the basis of enzyme histochemistry
Alkaline ATPase reaction Acid ATPase Reaction

26. Fibre size
Muscle Biopsy:
Sarcolemmal
nuclei
Fibre types
Inflammatory Cell
Necrosis
Other Structures

27. Dermatomyositis:
• Inflammation predominantly at
perivascular sites or within the interfascicular
septae
• Groups of muscle fibres undergo
phagocytosis and necrosis,
(microinfarcts) characteristically in the periphery of
the fascicle atrophy.
• Perifascicular atrophy-characterised by 2-10 layers
of atrophic fibres at the periphery of the fascicles.
• Involves both type1 and type 2 muscle fibers
• Skin lesions show perivascular inflammation with
CD4-positive cells in the dermis

28. Dermatomyositis:
Involvement of intramuscular blood vessels is characterized by:
(a) the deposition of immunoglobulin sand complement, including the C5b-C9
membrane attack complex (MAC), on endomysial capillaries and small blood vessels
(b) the reduction in number of capillaries in the perifascicular region
(c) endothelial hyperplasia and enlargement of the lumen of intramuscular capillaries
Humoral Microangiopathy

29. Dermatomyositis:
Tubuloreticular cytoplasmic inclusions (TRIs)
are often seen in endothelial cells.

30. Polymyositis:
• Increased variation in fiber diameter,
• Scattered necrotic and regenerating muscle fibers
•Mononuclear inflammatory cells that surround, invade destroy muscle fibres
•Multifocal lymphocytic infiltrates Predominantly of cytotoxic CD8 T cells along with a
lesser number of macrophages and few CD4 T cells.
•Chronic stages show increase in permysial and endomysial connective tissue.

31. Inclusion Body Myositis:
• Inflammatory cells consisting predominantly of macrophages and CD8 T cells which
invade nonnecrotic muscle fibers .
• Endomysial inflammation
•Fibre hypertrophy and fibre splitting.
• Nonnecrotic muscle fibers with 1/>1 or more,
irregular and various-sized vacuoles with basophilic
granular deposits around the edges (rimmed
vacuoles)
Modified Gomori trichrome Stain.

32. Inclusion Body Myositis:
• Single or multiple intracellular amyloid deposits,
identified with fluorescence-enhanced Congo red
staining
• Eosinophilic cytoplasmic inclusions, usually
near or in the vacuoles
Granules consist of myelinoid membranous bodies

33. Immune mediated necrotising Myopathy:
• Presence of randomly distributed necrotic muscle fibers along with fibers in various
stages of regeneration, and in absence of or sparse mononuclear cell infiltrates.
• Necrotic fibers may be invaded by macrophages
• Weak and focal MHC class I antigen may be expressed.
• Deposition of MAC on intramuscular blood vessels may be seen.
• Muscle biopsy lacks the typical diagnostic features of DM and of PM

34. Inflammatory myopathy with Abundant Macrophages:
• Described initially in 2009 by Brunn et al; thought to be a variant of dermatomyositis
• Presents with proximal muscle weakness and skin rash
• May be accompanied by raynaud phenomenon and arthralgias.
•Typically CK elevation is minimal or near normal
• Diffuse destructive infiltration of macrophages into the fascia
• Thickening of fascia and cellular inflammation.
• Infitration of CD68-positive macrophages abundant

35. Inflammatory myopathy with Abundant Macrophages:
CD4 CD8
CD68
CD20

36. Serology:
• Auto-antibodies are powerful diagnostic and prognostic tools in IIM.
• Found in 80% of patients with IIM directed against intra-cellular constituents.
• Multianalytic line blot assay.
Myositis Associated AntibodiesMyositis Specific Antibodies

37. Myositis Specific Antibodies
• 90% diagnostic specificity
• Target cytoplasmic or nuclear
ribonucleoproteins
Myositis Associated Antibodies
• 50 % of myositis patients,
• Not disease-specific
• Associated with MSA
• found in myositis overlap syndrome,
primarily myositis-systemic sclerosis
(PDM/SSc)
Serology:

38. Serology:

39. Serology:
•Myositis Specific Autoantibodies:
•8 tRNA synthetases have been identified
•Anti-Jo-1 is the most common, found in 20–
30 % of patients with PM and 60–70 % of
myositis patients with interstitial lung disease
• Severe necrotizing myopathy,
histologically characterized by abundant
myofiber necrosis and regeneration, with
scarce inflammation.

40. Muscle biopsy inclusion and exclusion criteria
a. Endomysial inflammatory cell infiltrate (T-Cells) surrounding and invading non-
necrotic muscle fibres
b. Endomysial CD8 + T-cells surrounding, but not definitely invading non-necrotic
muscle fibres, or ubiquitous MHC-1 expression
d. MAC depositions on small blood vessels, or reduced capillary density, or
tubuloreticular inclusions in endothelial cells on EM, or MHC-1 expression of
perifascicular fibres
e. Perivascular, perimysial inflammatory cell infiltrate
f. Scattered endomysial CD8 + T-cells infiltrate that does not clearly surround or
invade muscle fibres
g. Many necrotic muscle fibres as the predominant abnormal histological feature.
Inflammatory cells are sparce or only slight perivascular; perimysial infiltrate is not
evident.
h. Rimmed vacuoles, ragged red fibres, cytochrome oxidase-negative fibres that
would suggest IBM
i. MAC deposition on the sarcolemma of nonnecrotic fibres and other indications of
muscular dystrophies with immunopathology

41. Dimachkie MM, Barohn RJ. Inclusion body myositis. Neurol Clin. 2014 Aug;32(3):629-46, vii. doi:
10.1016/j.ncl.2014.04.001. Epub 2014 Jun 6. Review. x