October 27, 2010

Q&A: Anterior Horn Cell Degeneration As Mechanism Of Disease

Neuromuscular disorders often present with hypotonia and weakness. These disorders are caused by a variety of conditions that affect the central nervous system (brain or spinal cord), peripheral nervous system, or skeletal muscle. One of the mechanisms of diseases affecting the peripheral nervous system or skeletal muscle is the degeneration of the anterior horn cells of the spinal cord.

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In this article:
Anatomy: anterior horn cells of the spinal cord
MCQ: clinical scenario
MCQ: answer
MCQ: explanation

Anatomy: anterior horn cells of the spinal cord

Anterior horn cells (α-motor neurons), located in the anterior gray matter of the spinal cord, are found at every segment and are concentrated in the cervical and lumbosacral enlargements. Morphologic differentiation of the anterior horn cells is most evident from 12 to 14 weeks' gestation. There is a period of normal differentiation, followed by programmed cell death. Anterior horn cells are clustered into medial and lateral cell divisions.

The medial group is subdivided into ventromedial and dorsomedial components. The ventromedial component innervates the superficial larger muscles, and the dorsomedial component innervates the small, deep muscles adjacent to the spine. The lateral cell mass is also subdivided into groups. The ventrolateral group innervates extensor muscles, and the centrodorsal group innervates flexor muscles. These groups of neurons are located in a relatively small region; therefore deleterious influences harm cells from more than one group and weakness may be widespread.

Motor neurons in the nuclei of brainstem cranial nerves are homologous to spinal cord anterior horn cells. Therefore pathologic mechanisms that compromise the cranial motor neurons may initiate symptoms and signs that mimic anterior horn cell dysfunction in the spinal cord. Muscular atrophy, severe weakness, and fasciculations without sensory deficit are signs of anterior horn cell disease. When sensory function is impaired in conjunction with anterior horn cell disease, dysfunction of adjacent tracts of the spinal cord or the peripheral nerves may be present.

Many conditions, especially in the newborn, are caused by degeneration of the anterior horn cells of the spinal cord. They include spinal muscular atrophy, traumatic myelopathy, hypoxic-ischemic myelopathy, poliomyelitis, and neurogenic arthrogryposis.

MCQ: clinical scenario

Match the following mechanism or pattern with the appropriate disease.

Progressive degeneration of anterior horn cells resulting in progressive muscle weakness, wasting and fasciculations.

a) Guillain-Barré syndrome
b) Duchenne muscular dystrophy
c) Becker muscular dystrophy
d) Myasthenia gravis (MG)
e) Amyotrophic lateral sclerosis
f) Myotonic dystrophy

MCQ questions & answers on medicalnotes.info

MCQ: answer

The correct answer is E

MCQ: explanation

Amyotrophic lateral sclerosis is a progressive neuromuscular condition characterized by weakness, muscle wasting, fasciculations and increased reflexes. The disease is most commonly diagnosed in middle age and affects more men than women. It usually presents with problems in dexterity or gait resulting from muscle weakness. Difficulty in speaking or swallowing is the initial symptom in the bulbar form of the disease.

Over a period of months or years, patients with ALS develop severe, progressive muscular weakness and other symptoms caused by loss of function in both upper and lower motor neurons. Sphincter control, sensory function, intellectual abilities and skin integrity are preserved. Patients become completely disabled, often requiring ventilatory support and gastrostomy. Death usually occurs within five years of diagnosis and is attributed to respiratory failure or cachexia.

Reference(s)
1). ScienceDirect: Anterior Horn Cell - an overview. Available online: https://www.sciencedirect.com/topics/medicine-and-dentistry/anterior-horn-cell

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