2. • Muscle is a specialized type of C.T
• Three types of muscle tissue can be identified
on the basis of structure, contractile
properties, and control mechanisms into:
1. Skeletal M.
2. Smooth M.
3. Cardiac M.
3. 1) Skeletal muscle:
• Attached to the skeleton.
• Muscle fibers are tubular, multinucleated, and
striated.
(Striation from thick myosin with thin actin myofibres)
• Voluntary in action.
4. 2) Smooth muscle:
• An integral part of many internal organs
(stomach, intestines, U.B, uterus, B.V, and airways)
• Muscle fibers are spindle-shaped, uninucleated
and non-striated
•Involuntary in action, controlled by A.N.S &
hormones
5. 3) Cardiac muscle:
• Forms the heart.
•Muscle fibers are tubular, branched,
uninucleated, and striated.
•Involuntary in action, determined by specialized
pace maker cells in the SAN
6. Physiology:
• All three muscle types use the movement of
actin against myosin to create contraction.
• All skeletal muscle and many smooth muscle
contractions
are
facilitated
neurotransmitter acetylcholine
by
the
• Proper muscle contraction needs contractile
myofibrils (actin & myosin) together with
calcium and ATP.
14. LABORATORY INVESTIGATIONS OF MUSCLE DISEASES
Preliminary investigations
II.
Enzyme activities
III.
Proteins
IV.
Antibodies testing
V.
Other laboratory tests that might aid in the diagnosis
VI.
Immunohistochemistry
VII. Genetic studies
VIII. Skeletal muscle biopsy
IX.
Special tests
I.
15. I) Preliminary investigations
1) Complete blood picture:
Anemia: associates systemic diseases, phosphofructokinase
deficiency (hemolytic),
Leukocytosis: polymyositis and dermatomyositis
Eosinophilia: polymyositis
2) ESR & CRP:
Elevated in polymyositis, dermatomyositis and during activity
of collagenic diseases.
3) Creatine & Creatinine:
Elevated serum creatinine: rhabdomyolysis, scleroderma,
sarcoidosis,
Elevated urine creatine: Myopathy associated with alcoholism
Elevated creatine/creatinine ratio: Muscular Dystrophies,
active muscle diseases.
16. 4) Electrolytes:
Serum calcium:
When decreases causes muscle rigidity and tetany.
When increases causes muscular hypotonia.
Serum potassium:
Increases: malignant hyperthermia (> 7 mEq/L), hyperkalemic
familial periodic paralysis (may reach values > 8 mEq/L).
Decreases: hypokalemic familial periodic paralysis (< 2 mEq/L)
5) Arterial blood gases:
1) Combined metabolic and respiratory acidosis
Malignant Hyperthermia
(Diagnostic in the presence of muscle rigidity or rising temperature)
2) Increased pCo2:
Indicates progressive respiratory failure in Myasthenia Gravis
3) Early respiratory alkalosis then respiratory acidosis follows:
Bronchial asthma
17. II) Enzyme activities
A)
Primary muscle enzymes:
1. Creatine kinase (mainly CK-MM): test of choice
•Increased in:
- Prolonged exercise
-Polymyositis
{the most useful diagnostic test. Increased in 70% of patients. Levels may vary greatly,
up to 50 X ULN. The level frequently becomes normal with steroid therapy}
-Duchenne muscular dystrophy
{always increased in affected children (5–100X ULN of adults) to peak by 2 years of age;
then begin to fall as disease becomes manifest. In fact, persistent normal CK virtually
rules out this diagnosis. Not affected by steroids}
-Facioscapulohumeral Dystrophy
{ mildly increased in 75% of patients to average 3X ULN}
-Limb-Girdle Dystrophy
{increased in 70% of patients to average of 10X ULN}
-Myotonic dystrophy
{ mildly increased in 50% of patients to average 3X ULN}
18. - Acute myopathy associated with alcoholism
{increased in 80% of patients; rises in 1 to 2 days; reaches peak in 4 to 5 days; lasts ~2
weeks}
- Chronic myopathy associated with alcoholism
{ increased in 60% of patients to average of 2X ULN}
- Malignant hyperthermia
{up to 20,000 - 100,000 U/L}
- Rhabdomyolysis
{ up to 20 X ULN which rises and falls rapidly}
• Normal in:
- Scleroderma
- Familial periodic paralysis
- Discoid lupus
- Muscle atrophy of neurologic origin (e.g., old poliomyelitis, polyneuritis)
- Hyperthyroid myopathy
•
Decreased in:
- Rheumatoid arthritis (~2/3 of patients)
19. 2. CK-MB:
Skeletal Muscle Disorders That May Cause Increased Serum CK-MB:
(Reflecting its production by regenerating muscle)
Malignant hyperthermia
Alcoholic myopathy
Dermatomyositis/polymyositis
Duchenne muscular dystrophy
Exercise myopathy
Familial hypokalemic periodic paralysis
Endocrine (e.g., hypoparathyroidism, acromegaly)
Rhabdomyolysis
Infections
Severe skeletal muscle trauma
20. 3) Aldolase:
Marked increase in Rhabdomyolysis
Elevated in 75% of cases of polymyositis and 20% of cases of
muscular dystrophy.
4. Lactate Dehydrogenase:
LD-5 is the iso-enzyme that is elevated in skeletal muscle
diseases.
Marked increase in Rhabdomyolysis
Elevated in 25% of cases of polymyositis and 10% of cases of
muscular dystrophy.
5. AST:
Marked increase in Rhabdomyolysis (> 3000 IU/L)
Elevated in 25% of cases of polymyositis and 15% of cases of
muscular dystrophy.
21. B) Specific enzymes:
1. Angiotensin-converting enzyme:
- Elevated in sarcoidosis
2. Carnitine palmitoyltransferase deficiency (Lipid storage diseases):
22. CPT I and CPT II are essential for the transport of long-chain
fatty acids from the cytosol to the mitochondria.
It is the most commonly identified metabolic cause of recurrent
myoglobinuria (dark urine) in adults.
Patients often have episodes of muscle pain, stiffness, and
tenderness, usually without frank cramps. The attacks are
triggered by prolonged exercise, especially in fasting
conditions.
May cause a severe and fatal disease in the neonatal period
and during early infancy characterized by hypoketotic
hypoglycemia.
Plasma carnitine level may be increased in CPT I deficiency,
but it is usually normal in CPT-II deficiency.
Final diagnosis usually is established through biochemical
demonstration of CPT deficiency in the muscle.
CPT deficiency should be differentiated from glycogen storage
diseases, particularly McArdle disease.
23. 3) Glycogen storage diseases (glycogenoses):
Deficiency of the following enzymes is biochemically detected in muscles:
Glycogenosis type II - Acid maltase deficiency (AMD); Pompe disease.
Glycogenosis type V - Muscle phosphorylase deficiency; McArdle disease.
Glycogenosis type VII - Phosphofructokinase deficiency; Tarui disease.
Glycogenosis type IX - Phosphoglycerate kinase deficiency.
Glycogenosis type X - Phosphoglycerate mutase deficiency.
24.
25. III) Proteins:
A. Myoglobin:
Urinary and serum Myoglobin is elevated in:
Rhabdomyolysis
Carnitine palmitoyltransferase deficiency
Trauma
Malignant hyperthermia
Polymyositis / Dermatomyositis
Duchenne muscular dystrophy & Facioscapulohumeral dystrophy
Myopathy associated with alcohol intake
Myoglobin clearance:
A value below 4 ml / min suggests high incidence for developing
ARF in patients with rhabdomyolysis. (Earlier than CCl)
26. B) Troponins:
Skeletal Troponin T and Skeletal troponin I, with its two distinct
isoforms (fast and slow), are elevated in:
Exercise induced muscle injury.
Myositis (suggested by some authors)
C) Dystrophin:
Dystrophin protein quantitated by Western blot on biopsy of muscle
is <3% of normal in Duchenne muscular dystrophy.
Immunofluorescence performed on biopsy of muscle is used to
confirm WB results in patients with suspected dystrophinopathy.
D) Alpha1-antitrypsin:
Its serum level decreases in emphysema patients.
27. IV) Antibodies testing:
A) Antibodies in Myasthenia Gravis (MG): (RIA & Radioreceptor assay)
1. Acetylcholine Nicotinic Receptor-Binding Antibodies
The standard assay and should be ordered first.
Has a sensitivity of 80 – 96 % and a specificity > 99 %.
Negative in about 50 % of cases with ocular MG>
Correlates with severity and ameliorated by treatment.
2. Acetylcholine Nicotinic Receptor-Blocking Antibodies
More often associated with more severe forms of disease.
3. Acetylcholine Nicotinic Receptor-Modulating Antibodies
Positive in 7% of MG patients when AChR-binding antibodies are not detected.
4. Antibodies to skeletal muscle cross-striations
Found in 30% of adult MG patients.
5. Antibodies against Muscle Specific Kinase
Present in about 50 % of sero-negative patients.
6. Other antibodies
Anti-DNA, ANA, anti-parietal cell, anti-smooth muscle, antimitochondrial,
antithyroid antibodies, rheumatoid factor.
28. B) Antibodies against P/Q voltage-gated calcium channel:
- In Lambert-Eaton syndrome.
- D.D from MG.
C) Myositis specific auto antibodies: (ELISA, IF & immunoprecipitation)
Anti Ro-52, anti Jo-1, anti Mi-2, anti SRP,
anti PM / Scl-100, anti PM / Scl-75
D) Antibodies in scleroderma:
Anti-DNA, Anti-La/SS-B, Antinuclear antibody, Anti-RNP, Anti-Sm test.
29. V) Other laboratory tests that might aid in the diagnosis:
1) Urine cytology and toxicology screening: rhabdomyolysis
2) Fecal leukocytes and occult blood: diverticulosis
3) HLA B 27: MG
4) D-xylose test in serum or urine: scleroderma
5) CSF Immunoglobulin G ratios and immunoglobulin G index:
MS
6) Carnitine level: decreases in muscles and plasma on
carnitine deficiency myopathy.
30. VI) Immunohistochemistry:
1) Myeloid-related proteins MRP8 and MRP14:
Calcium binding proteins expressed in inflammatory myopathies
2) Ki-67 proliferation protein:
- Cellular marker of proliferation detected immunohistochemically
by a monoclonal antibody.
- Expressed in sarcoidosis.
3) Smooth muscle markers:
- Smooth muscle α-actin (α-SMA): in Chronic idiopathic intestinal
pseudo-obstruction
- Smooth muscle myosin heavy chain (SMMHC): in
gastrointestinal motility disorders
- Smoothelin (SM): in gastrointestinal motility disorders
- Histone deacetylase 8 (HDAC8): in gastrointestinal motility
disorders
32. 5) Glycogen storage diseases:
Glycogenosis type II : autosomal recessive (17q23)
Glycogenosis type V(McArdle disease): autosomal recessive (11q13)
Glycogenosis type VII: autosomal recessive (12q13.3)
Glycogenosis type IX: X-linked recessive (Xq13)
Glycogenosis type X: autosomal recessive (11p15.4) (isozyme LDH-M on
chromosome 11/ LDH-H on chromosome 12)
6) Bronchial asthma:
- ADAM33 gene located on chromosome 20 and is expressed in lung and
muscle cells.
It is believed to be related to asthma as it causes the airways to over-respond
and constrict airway passage.
- Other genes: PHF11, DPP10, GRPA & SPINK5
(Their functions are still obscure)
33. VIII) Skeletal muscle biopsy: (Confirmatory)
- Muscular dystrophy: fibers necrosis, regeneration and
replacement by fat.
- Mitochondrial diseases: ragged red muscle fibers.
- Polymyositis: inflammatory changes with mononuclear
cells infiltration.
- Myopathic carnitine deficiency: increased number of lipid
droplets with minimal or no increase in mitochondria.
- Glycogenosis type V(McArdle disease): glycogen
accumulation in muscle fibers.
34. IX) Special tests:
1) Malignant Hyperthermia: (inhalation anesthesia, increase
calcium, M. rigidity)
- Gold standard for diagnosis by in vitro exposure of biopsied
skeletal muscle to caffeine-halothane contracture test; S/S =
99%/94%.
2) Edrophonium test:
- Its application is limited to the situation when other investigations
do not yield a conclusive diagnosis about MG.
- This test requires the intravenous administration of edrophonium
chloride (Tensilon), a drug that blocks the breakdown of
acetylcholine by cholinesterase and temporarily increases the
levels of acetylcholine at the neuromuscular junction.
- In people with myasthenia gravis involving the eye muscles,
edrophonium chloride will briefly relieve weakness.
35. 3) Forearm ischemic exercise test:
- To D.D glycogen and lipid storage diseases.
Technique
- Draw venous blood for lactate as baseline samples.
- Apply a sphygmomanometer on the arm to be tested and raise its
pressure slightly above the systolic blood pressure.
- Ask the patient to exercise repetitively for 1 minute.
- Stop exercise, deflate the sphygmomanometer, and draw blood
samples at 1, 3, 6, and 10 minutes after 1 minute of exercise for
lactate and ammonia.
Findings
- In healthy subjects, lactate level should increase to 3-5 times the
basal level in the first 2 samples after exercise and then decrease
gradually to the baseline.
- In glycogen storage diseases, such as McArdle disease, serum
lactate levels do not increase after exercise (ie, flat lactate curve),
while in lipid storage diseases, lactate and level increase in a normal
fashion.