Sunday, June 18, 2017

CMS neurology form 2: Question on numbness, tingling and decreased grip strength

Disclaimer: This is an CMS neurology form 2 question for step 2 CK. If you are planning to take USMLE step 2 CK in the future, I would recommend that you DO NOT read this post because it will bias your assessments.

A 52 year old man presents with a 1 month history of numbness and tingling of the ring and small fingers of his right hand that radiates to his palm. His symptoms are not constant and exacerbated at night. He has a 2 week history of decreased grip strength and wasting of the small muscles in his right hand. He has not had neck or arm pain. 4 months ago, he was diagnosed with pancreatic cancer, since then, he underwent Whipple procedure and is currently receiving chemotherapy with gemcitabline. Since his diagnosis, he has had significant fatigue and an 18 kg weight loss. He is 173 tall and weighs 54kg. BMI is 18. His temp is 37, pulse is 95, and BP is 120/79. There is wasting of the interosseous muscles on the right. Muscle strength is 3/5 in the right interosseous and hypothenar muscles and flexor digitorum profundus of the ring and small fingers. It is full elsewhere. Deep tendon reflexes are 2+ throughous. Babinski sign is absent. Sensation to pinprick and temperature is decreased over the ulnar aspect of the palm and dorsum of the hand ring and small fingers; proprioception is intact. The remainder of the neurologic exam shows no abnormalities. Which of the following is the cause of his symptoms?
A. C8 nerve root infiltration by tumor
B. Cervical disc herniation
C. Chemotherpay neurotoxicity
D. Ulnar nerve compression
E. Vit B12 deficiency

Confusing answer choices: C8 root infiltration by tumor infiltration vs ulnar nerve compression.
The weakness pattern given is conforming to ulnar nerve rather than C8 myotomes. Root pain is generally present in radiculopathies. Also, in C8 radiculopathy, sensory and motor involvement will be more extensive. Triceps reflex would be affected in C8 radiculopathy.

Obvious incorrect answer choices:
Cobalamin deficiency is a generalized peripheral neuropathy. Vibration sense is one of the earliest to go.
Chemotherapy induced neuropathy also is generalized polyneuropathy and has preponderance of sensory symptoms.
The absence of neck pain makes the possility of cervical spondolysis less likely. Also, cervical spondylosis is most common in C5 C6 though it can rarely occur in C7 C8.
Doubt: Why is there no loss of proprioceptive sensation?
Please note that the author of this question has said that there is decreased senstion and not complete anesthesia.
Thus, patient can percieve vibration (present or absent) while testing and feel the decreased sensation of pinprick, temperature by comparison with the normal area.
Generally, when we do vibration test with a tuning fork, all we ask the patient is can he feel it and we ask the patient to indicate when the vibrations stop. But in pinprick, we ask the patient to compare with a normal sensation in a normal area.
Extra: In ulnar nerve compression, Froment's sign, tests for palsy of the ulnar nerve, specifically, the action of adductor pollicis. It isn't mentioned in this question but worth knowing.
This was explained by a Medicowesomites (Upsana's) professor. Thank you, Dr Pankaj Kumar for taking the time and explaining this question and the doubt in such detail. Also, thank you for letting me make a few edits and publish this. It'll be helpful to a lot of students!
-IkaN

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