10-04-2006, 05:16 PM
13. A 45-year-old male is brought to the Emergency
Department by his family, who have
noted him to be behaving bizarrely. There is a
family history of early death. He is unable to
control pronounced choreiform movements of
his upper extremities and trunk. Which of the
following is the most likely neurotransmitter
disturbance?
(A) Depletion of acetylcholine
(B) Depletion of dopamine
© Depletion of γ-aminobutyric acid
(D) Excessive production of acetylcholine
(E) Excessive production of dopamine
(F) Excessive production of γ-aminobutyric
acid
(G) Excessive production of norepinephrine
© is correct. Huntington™s disease is an autosomal
dominant disorder characterized by involuntary
choreiform movements, cognitive disturbance, and
emotional dysfunction. Onset is in the fifth decade.
There is atrophy of the caudate nucleus with depletion
of γ-aminobutyric acid.
Explanation A: No. There is a postulated role for
depletion of acetylcholine in the pathophysiology of
Alzheimer™s disease.
Explanation B: No. There is a postulated role for the
depletion of dopamine in the pathophysiology of
Parkinson™s disease.
Explanation D: No. Acetylcholine does not play a role
in the pathophysiology of Huntington™s disease.
Explanation E: No. Dopamine does not play a role in
the pathophysiology of Huntington™s disease. Excessive
amounts of dopamine are postulated to play a role in
schizophrenia.
Explanation F: No. Excess of γ-aminobutyric acid does
not play a role in the pathophysiology of Huntington™s
disease.
Explanation G: No. Norepinephrine does not play a
role in the pathophysiology of Huntington™s disease.
14. A 24-year-old female presents to her primary
care physician with complaints of weakness
and fatigue, worse in the afternoons for the last
several months. The fatigue is relieved with a
short nap. She has prominent bilateral ptosis.
Which of the following is the target of the
autoantibodies in this disease?
(A) Acetylcholinesterase
(B) Muscle fiber acetylcholine-gated ion
channels
© Muscle fiber membrane
(D) Nerve fiber calcium channels
(E) Nerve fiber membrane
(B) is correct. Myasthenia gravis is an autoimmune
disease characterized by muscle weakness.
Autoantibodies block the binding of acetylcholine to
muscle fiber ion channels causing end-plate potentials
too weak to properly stimulate muscle fibers.
Explanation A: No. Diisopropyl fluorophosphate (a
nerve gas) as well as neostigmine and physostigmine
inactivate acetylcholinesterase, causing repetitive
stimulation of muscle fibers and spasm, not weakness.
Explanation C: No. The target of the autoantibodies
in myasthenia gravis is not the muscle fiber membrane.
Explanation D: No. The target of the autoantibodies
in myasthenia gravis is not the nerve fiber calcium
channels.
Explanation E: No. The target of the autoantibodies in
myasthenia gravis is not the nerve fiber membrane.
Department by his family, who have
noted him to be behaving bizarrely. There is a
family history of early death. He is unable to
control pronounced choreiform movements of
his upper extremities and trunk. Which of the
following is the most likely neurotransmitter
disturbance?
(A) Depletion of acetylcholine
(B) Depletion of dopamine
© Depletion of γ-aminobutyric acid
(D) Excessive production of acetylcholine
(E) Excessive production of dopamine
(F) Excessive production of γ-aminobutyric
acid
(G) Excessive production of norepinephrine
© is correct. Huntington™s disease is an autosomal
dominant disorder characterized by involuntary
choreiform movements, cognitive disturbance, and
emotional dysfunction. Onset is in the fifth decade.
There is atrophy of the caudate nucleus with depletion
of γ-aminobutyric acid.
Explanation A: No. There is a postulated role for
depletion of acetylcholine in the pathophysiology of
Alzheimer™s disease.
Explanation B: No. There is a postulated role for the
depletion of dopamine in the pathophysiology of
Parkinson™s disease.
Explanation D: No. Acetylcholine does not play a role
in the pathophysiology of Huntington™s disease.
Explanation E: No. Dopamine does not play a role in
the pathophysiology of Huntington™s disease. Excessive
amounts of dopamine are postulated to play a role in
schizophrenia.
Explanation F: No. Excess of γ-aminobutyric acid does
not play a role in the pathophysiology of Huntington™s
disease.
Explanation G: No. Norepinephrine does not play a
role in the pathophysiology of Huntington™s disease.
14. A 24-year-old female presents to her primary
care physician with complaints of weakness
and fatigue, worse in the afternoons for the last
several months. The fatigue is relieved with a
short nap. She has prominent bilateral ptosis.
Which of the following is the target of the
autoantibodies in this disease?
(A) Acetylcholinesterase
(B) Muscle fiber acetylcholine-gated ion
channels
© Muscle fiber membrane
(D) Nerve fiber calcium channels
(E) Nerve fiber membrane
(B) is correct. Myasthenia gravis is an autoimmune
disease characterized by muscle weakness.
Autoantibodies block the binding of acetylcholine to
muscle fiber ion channels causing end-plate potentials
too weak to properly stimulate muscle fibers.
Explanation A: No. Diisopropyl fluorophosphate (a
nerve gas) as well as neostigmine and physostigmine
inactivate acetylcholinesterase, causing repetitive
stimulation of muscle fibers and spasm, not weakness.
Explanation C: No. The target of the autoantibodies
in myasthenia gravis is not the muscle fiber membrane.
Explanation D: No. The target of the autoantibodies
in myasthenia gravis is not the nerve fiber calcium
channels.
Explanation E: No. The target of the autoantibodies in
myasthenia gravis is not the nerve fiber membrane.