Neurological Disorders: Myopathy

Introduction

Myopathy is the medical term used for muscle diseases of any kind. There are various types depending upon what causes the muscle damage and is not an uncommon neurological disorder.

Anatomical issues

Human body has 3 types of muscles; skeletal muscle, cardiac (heart) muscle & smooth muscle types.

Skeletal muscles are also called as voluntary muscles since we have a good amount of voluntary control on their movements e.g. we bend our elbow when we voluntarily activate (contract) the biceps muscle which is an example for the above category. The other two types of muscles are not under our voluntary control.

The above term can be used for diseases of heart & smooth muscles too. However in general they are not managed by the neurologists, rather doctors specialized in the respective fields (e.g. cardiologists, internists, GI specialist etc).

So from here onwards the discussion will focus only on diseases of the skeletal muscles.

What causes muscle diseases?

There are myriad causes for muscle diseases and include;

• Congenital (person born with it)
• Inflammatory (e.g. polymyositis, dermatomyositis)
• Genetic (e.g. muscular dystrophies like Duchenne; Channelopathies like Periodic Paralysis )
• Traumatic
• Metabolic / Endocrine disorders (e.g. hypothyroidism)
• Toxin exposure (e.g. chronic alcohol consumption)
• Medication induced (e.g. steroid myopathy)
• Infections (e.g. AIDS virus, parasitc infections etc)

How does patient present?

• Muscle weakness
• Muscle atrophy (thinning)
• Difficulty with using limbs due to weakness

Some relatively common muscle diseases

• Polymyositis
• Inclusion body myositis
• Myotonic dystrophy

Diagnosis

The following neurology tests are generally required to establish the diagnosis of muscle diseases(tests decided on case to case basis);

• Blood tests like CPK, LDH
• EMG/NCS (electromyography & nerve conduction studies)
• Muscle biopsy
• Genetic testing etc

Treatment

The treatment will depend upon the individual condition. In general the following are the important therapeutic interventions;

• If medication or toxin induced stop the offending agent
• Steroid therapy (e.g. prednisolone, methyl prednislone etc)
• Other immunosuppressive agents like azathioprine, cyclosporine etc
• Intravenous immunoglobulins
• Plasmapheresis
• Experimental therapies like gene or stem cell therapies (especially for muscular dystrophies)
• Treatment of underlying infections like HIV, parasites like trichinosis
• Physically therapy as required & tolerated
• Symptomatic therapy for muscle pain with pain killers; if myotonia is present then anti-myotonia agents like phenyoin, mexelitine etc.

A neurologist is commonly involved in the care of patients with muscle diseases.

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