Neuromuscular Diseases

Neuromuscular disease is a broad term that encompasses many diseases and ailments that impair the functioning of the muscles. These may directly involve the muscle directly or indirectly by involving the nerves or the neuromuscular junction (the meeting point of the motor nerves and muscle fibre). The symptoms of neuromuscular diseases may include- Numbness, painful abnormal sensation, muscle weakness, muscle atrophy, muscle pain or twitching (fasciculation). The Neuromuscular diseases may be categorized into the following groups:

  • Diseases of Anterior Horn Cells (Junction between spinal cord and motor nerve)
  • Diseases involving motor and sensory nerves – Peripheral Neuropathies
  • Disorders of the Neuromuscular function – Myasthenia Gravis and related diseases
  • Diseases of the muscles (Myopathies)- Muscular Dystrophy and Inflammatory myopathies

Motor Neuron Diseases

These are characterised by progressive degeneration and loss of motor neurons in the spinal cord, with or without similar lesions in motor nuclei of the brainstem. The cells lost are replaced by gliosis (scar tissue). The term Motor Neurone Diseases (singular) is however reserved for the adult disease - Amyotrophic Lateral Sclerosis (ALS) in which both upper and lower motor neurons are affected. In ALS, the weakness may commence in the leg, hands, proximal arm or oropharynx (slurred speech or difficulty in swallowing). Often the hands are affected first, mostly asymmetrically. Painless difficulties with buttoning or turning of a key are ominous symptoms in midlife. Fasciculation may be seen in the tongue and proximal muscles of upper limb.

Peripheral Neuropathies

This is a term used to describe syndrome resulting from diffuse lesions of the peripheral nerves, usually manifested by weakness, sensory loss, pain and autonomic dysfunction. ‘Neuritis’ is a term typically reserved for inflammatory disorder of the nerves, resulting from infection or autoimmunity. Symptoms of polyneuropathy include acral pain, paraesthesia, weakness and sensory loss. The pain may be spontaneous or elicited by stimulation of the skin and may be sharp or burning. Paraesthesias are usually describes as numbness, tingling, buzzing, burning or a feeling of constriction. In these patients a detailed family, social, medical and drug history in addition to thorough examination, followed by NCV / EMG and other lab tests, is needed to clinch the diagnosis. Some of the common causes in India include- Immune mediated (GuillainBarre Syndrome), B12 deficiency, Diabetes, Drug related, toxins and Renal failure.

Disorders of Neuromuscular Junction

Muscle diseases caused by a defect of Nerve Signal transmission owing to antibody medicated attack or acetyl- choline receptors at Neuromuscular junction. The abnormal antibodies are produced in the thymus gland and bone marrow. The characteristic fluctuating nature of the myasthenic weakness is unlike any other disease.

The weakness varies in the course of a single day, sometimes within minutes and it varies from day to day or over longer periods. It is usually worse towards the evening. The abnormal antibodies can be detected in the serum of around 85% of patients with generalized Myasthenia. Sometimes the condition can be localized to the eyes and is called Ocular Myasthenia. Drugs, Plasmaphareses, Intravenous Immunoglobulin, removal of thymus and steroids are various modes of treatment.

Progressive Muscular Dystrophies

These are primary, inherited, progressive degenerative disorders of muscle. The limbs-girdle, facial and sometimes the heart muscles may be affected and become weak. The disease shows slow, relentless progression, without any pain or sensory loss. The condition is recognized as heritable, even though there is no other case in the family. There is no curative therapy and gene therapy has not yet been successful, although for one of the common forms seen in childhood i.e. Duchenne Muscular Dystrophy, a disease modifying treatment is available. The disease characteristically involves muscles in one group in a selective manner. Diagnosis is by EMG and muscle biopsy.

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