Medicine Marrow Pg No 647-656 (Neurology)

Amyotrophic Lateral Sclerosis (ALS)

• ALS is a neurodegenerative disease affecting upper and lower motor neurons.
• 90% of cases are sporadic and 10% are genetic, often due to copper-zinc superoxide dismutase defects.
• ALS typically affects individuals over 50 years old, with males affected more frequently than females.
• Average survival after onset is 3 years.
• Primary structures affected include the anterior horn cells, lower motor neurons in brainstem nuclei, upper motor neurons in the corticospinal tract, and the corticobulbar tract.
• Clinical features include distal asymmetric upper limb atrophy, fasciculations, cramps, brisk reflexes, and loss of dexterity or tone.
• Cognition, the autonomic nervous system, and sensory systems remain intact.

Spinal Cord

• The spinal cord is a continuation of the medulla, extending from the upper border of the atlas (C1) to the junction between L1 and L2 in adults, or L3-L4 in children.
• 31 spinal cord segments correspond to the 31 pairs of spinal nerves.
• Each spinal nerve root is composed of a dorsal and ventral root.
• The spinal canal is 70 cm long, accommodating the spinal cord and its surrounding meninges (dura mater, arachnoid mater, and pia mater).

Spinal Cord Tracts

• Fasciculus cuneatus and fasciculus gracilis: Sensory tracts, involved in proprioception, fine touch, and pressure.
• Lateral corticospinal tract (pyramidal tract): Major motor pathway for voluntary movements.
• Dorsal spinocerebellar tract and ventral spinocerebellar tract: Carry sensory information related to proprioception.
• Lateral spinothalamic tract: Carries pain and temperature sensations.
• Ventral spinothalamic tract: Carries pressure and touch sensations.
• Rubrospinal tract: Influences movement.
• Lateral reticulospinal tract, ventral reticulospinal tract, and vestibulospinal tract: Involved in motor control and balance.
• Tectospinal tract: Controls reflexes related to eye and head movements.

Myelopathies

• Myelopathies are spinal cord diseases causing sensory, autonomic, and motor symptoms.
• Types of myelopathies:
  • Compressive:
    • Intramedullary: e.g. tumors (ependymoma) and syringomyelia.
    • Extramedullary: e.g. disc compression.
  • Non-compressive: e.g. transverse myelitis.
• Lesion Presentation:
  • Above the level of the lesion: Normal function.
  • At the level of the lesion: Symptoms depend on the involvement of anterior horn cells.
  • Below the level of the lesion: Motor (UMN-type) and sensory loss.

Grey Matter

• Anterior horn cells: Motor neurons responsible for voluntary movement.
• Level of lesion symptoms:
  • Motor symptoms (LMN-type): Absent reflexes are a key diagnostic feature.
  • Sensory symptoms: Vary based on the location of the lesion.

X-linked SMA (ALS Variants)

• Characterized by spinobulbar involvement, proximal muscle wasting, tongue wasting, and perioral fasciculations.
• May be associated with androgen insensitivity.

Benign Monomelic Amyotrophy (BMA)

• Also known as Hirayama disease.
• Primarily affects young males, causing weakness and atrophy in the upper extremity.
• Symptoms improve with rest and neck extension.

Myasthenia Gravis (MG)

• Autoimmune neuromuscular disorder affecting the neuromuscular junction.
• Characterized by fluctuating weakness in skeletal muscles.
• Primary cause is antibodies against the acetylcholine receptor (AChR) at the neuromuscular junction.
• 85% of cases are generalized MG.
• 50% of cases are ocular myasthenia.
• 10-20% of cases are generalized MG with negative anti-AChR antibodies.
• May involve thymus hyperplasia or thymoma in a significant proportion of cases.
• Thymectomy in adult-onset generalized MG has a good prognosis.

Lambert-Eaton Myasthenic Syndrome (LEMS)

• Autoimmune disorder affecting the release of acetylcholine from presynaptic motor neurons.
• Primarily affects proximal lower limbs and autonomic nervous system.
• Associated with small cell lung cancer in a significant number of cases.
• Antibodies target voltage-gated calcium channels on the presynaptic membrane.
• Treatment includes 3,4-diaminopyridine and supportive measures.

Myasthenia Gravis: Clinical Features

• Initial weakness, fatigue, and ptosis are characteristic features.
• Can involve bulbar muscles causing difficulty with speech and swallowing.
• Diurnal variation with worsening symptoms towards the evening.
• Muscle weakness increases with repetitive activity and improves with rest.
• Associated antibodies can be detected.
• Thymectomy can be beneficial in specific cases.
• Treatment options include cholinesterase inhibitors, immunosuppressants, and plasmapheresis.

Myasthenia Gravis: Investigations

• Clinical tests: Ice pack test, edrophonium test, and neostigmine test.
• Immunological tests: Anti-AChR antibody, anti-muscle specific kinase antibody, and anti-LRP4 antibody.
• Electrophysiological studies: Single nerve fiber electromyography, repetitive nerve stimulation test, and nerve conduction studies.

Bulbar vs. Pseudobulbar Palsy

• Bulbar palsy: Affects lower motor neurons of cranial nerves 9, 10, 11, and 12, causing dysphagia, dysarthria, and tongue fasciculations.
• Pseudobulbar palsy: Affects upper motor neurons to cranial nerves 9, 10, 11, and 12, resulting in spastic dysarthria, exaggerated reflexes, and emotional lability.

Conus Medullaris

• The terminal portion of the spinal cord located at the level of L1/L2 in adults and L3/L4 in children.
• Conus medullaris syndrome: Affects the sacral nerve roots and the conus medullaris, causing sacral sensory loss, urinary incontinence, and sphincter dysfunction.
• Cauda equina syndrome: Affects the lower lumbar and sacral nerve roots, leading to asymmetric radiculopathy, motor weakness, and variable sensory loss.

Anatomy of Spinal Cord

• The spinal cord extends from the medulla to the tip of the coccyx.
• Cervical enlargement houses the nerve roots for the upper limbs.
• Lumbar enlargement houses the nerve roots for the lower limbs.
• The filum terminale is a fibrous extension of the pia mater that extends from the conus medullaris to the coccyx.
• The dorsal tract (posterior column) carries sensory information for proprioception and tactile discrimination.
• The lateral spinothalamic tract carries pain and temperature sensations.
• Note:* This is a broad overview of the content. The text you provided does not include comprehensive explanations of specific syndromes and their management, so this summary focuses on highlighting key facts and anatomical features. Further research would be necessary for obtaining a complete understanding of these topics.