Myopathy



Myopathy is a term used to describe disorders of the muscle.  There are a number of conditions that affect the muscle.  Myopathies typically present with weakness of the proximal muscles such as the shoulders and hips.  Some present with easy fatigue.  Patients may complain of difficulty climbing stairs or fixing their hair in the morning. 

These disorder can be due to genetic disorders, inflammatory disorders and metabolic disorders among others.  This is a list of some of the most commonly encountered disorders.

  Tabulation of myopathies:

Congenital myopathies

1.       Central core disease
2.       Multicore disease
3.       Nemaline myopathy
4.       Centronuclear (myotubular) myopathy
5.       Congenital fiber-type disproportion
6.       Fingerprint body myopathy
7.       Rigid spine syndrome
8.       Reducing body myopathy
9.       Sarcotubular myopathy
10.    Zebra body myopathy
11.    Cytoplasmic body myopathy
12.    Cap disease


Muscular dystrophies

1.       Congenital
2.       Fukuyama
3.       Cerebro-ocular dysplasia
4.       X-linked recessive
5.       Pseudohypertrophic muscular dystrophy, severe (Duchenne)
6.       Pseudohypertrophic muscular dystrophy, mild (Becker)
7.       Emery-Dreifuss
8.       Facioscapulohumeral
9.       Limb-girdle syndrome
10.    Scapulohumeral (Erb)
11.    Childhood onset with recessive inheritance
12.    Late onset with dominant inheritance
13.    Quadriceps myopathy
14.    Distal myopathy
15.    Dominant inheritance:

                      i.      Welander
                      ii.      Non-Scandinavian

16.    Recessive inheritance
17.    Ocular myopathy
18.   Oculopharyngeal myopathy


Myotonic disorders

1.       Myotonic dystrophy
2.       Myotonia Glycopyrolate
3.       Chondrodystrophic myotonia (Schwartz-Jampel)
4.       Paramyotonia congenital


 Carbohydrate storage diseases

1.       Acid maltase deficiency (Pompe)
2.       Debrancher deficiency (Forbes)
3.       Brancher deficiency (Anderson)
4.       Phosphorylase deficiency (McArdle)
5.       Phosphofructokinase deficiency (Tarui)
6.       Phosphoglycerate kinase deficiency
7.       Phosphoglycerate mutase deficiency
8.       Lactic dehydrogenase deficiency
9.       Polyglucosan storage (Lafora)

 
Lipid storage diseases

1. Carnitine deficiency
2. Carnitine palmitoyltransferase deficiency
3. Acyl-CoA dehydrogenase deficiencies
4. Chanarai's disease
5. Batten's disease
6. Fabry's disease

 
Mitochondrial myopathies

Primary:

        Defective energy conservation
        Impaired substrate utilization
        Respiratory chain defects

Secondary:

        Ischemia
        Thyroid disease
        Glycogen storage disease
        Drug-induced

Endocrine myopathies

1.       Acromegaly
2.       Thyrotoxicosis
3.       Myxedema
4.       Cushing’s disease
5.       Exogenous steroid
6.       Hyperparathyroidism
7.       Hypoparathyroidism

 
Miscellaneous metabolic myopathies

1.       Alcohol-related disorders
2.       Malnutrition
3.       Chronic renal disease
4.       Amyloidosis
5.       Malignant hyperthermia
6.       Myoadenylate deaminase deficiency


Periodic paralysis

1.       Hypokalemic
2.       Hyperkalemic
3.       Normokalemic
4.       Thyrotoxic

 
Paraneoplastic disorders

1.       Motor neuron disease
2.       Radiculopathy/neuropathy
3.       Myasthenic syndrome
4.       Distal axon (twig) disease
5.       Inflammatory myopathies (polymyositis, dermatomyositis)
6.       Embolic


Toxic myopathies

1.       Alcohol
2.       Iron
3.       Chloroquine
4.       Clofibrate
5.       Glycoprotein
6.       EACA
7.       Emetine
8.       d-Penicillamine
9.       Pentazocine
10.    Vincristine
 

Inflammatory myopathies

1.       Infections
2.       Bacterial
3.       Fungal
4.       Viral
5.       Parasitic
6.       Immune-mediated
7.       Polymyositis
8.       Dermatomyositis
9.       Inclusion body myositis
10.    Myopathy in systemic connective tissue disease
11.    Eosinophilic fasciitis
12.    Polymyalgia rheumatica
13.    Sarcoidosis
14.    Idiopathic granulomatous myositis
15.    Drug-induced myopathies
16.    Eosinophilia myalgia syndrome (L-tryptophan myopathy)

Diagnosis:

The diagnosis of most myopathies involves a combination of laboratory studies and nerve conduction studies with specific testing of the muscles.  In most cases it is necessary to perform a muscle biopsy.  This is a very simple and minor outpatient procedure in which a small sample of a part of a muscle is removed from a small incision and subsequently analyzed by the pathologist.  The treatment will vary depending on the underlying cause of the myopathy.

Hypokalemic periodic paralysis:

Myotonic Dystrophy: