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NBME form 12 section 2 answers - djt
#11
10 is C , not B
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#12
Hey #39 is wrong. I also put C and it came out as wrong. Ill post the question on here:

In a patient with chronic peripheral neuropathy, enzyme histochemical staining of a muscle biopsy shows fiber grouping. Which of the following is most likely cause of this finding?

a) altered expression of muscle enzyme due to damaged nerve fibers
b) altered trophic substance from the innervating neurons
c) regeneration of muscle fibers (WRONG ANSWER)
d) reinnervation of muscle fibers by regenerating axons
e) selective loss of nerve fibers to type II muscle fibers
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#13
Re:NBME12,number 39, please any one know the answe
#2398633
yeabiruh - 05/20/11 05:10

Hi there ....
Chronic peripheral neuropathies bring myopatholgical changes in respective muscle groups that lost or regain innervation (secondary to the chronic peripheral neuropathies )......

-The most common changes in dennervation are atrophic fibres and fibre groups....
Reinnervation takes place in the chronic neuropathies......type grouping is a feature of reinnervation ....

-Hence histopatholgical changes of chronic peripheral neuropathies include both of the ABOVE....

-What is type grouping....remember muscle has type I and II fibers (A 5 dollar word for cell)...normally type I and Type II arrange like Checkerboard" pattern of type I (Light) and II (Dark) fibers....but in type grouping Type I and type II muscle fibers are
clustered in large groups (Type I together and Type II together )...

-Type grouping signifies clustering of muscle fibres of the same metabolic type, and is a frequent finding in reinnervated muscles.....


-Reinnervation occurs spontaneously in most cases. Usually this happens by having a nearby nerve grow a new axon that will gradually take over the deinnervated tissue....

hence choice D is the most likely answer....

the key word is knowing what TYPE GROUPING IS ....And know reinnervation causes it...
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#14
What is the Dx in Q 41? im so lost in that one!!! help
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#15
for 38, you meant "38 D Oligodentdrocytes (MS)" not C
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#16
31 is ancylostoma ( cutaneous larva migrans)
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#17
Q 35 TALKS ABT CASES AND CONTROL....
they are studying association b/w familial polyposis and colorectal cancer

I think answer should be C (NOT D) 'coz FAMILIAL POLYPOSIS IS THE RISK FACTOR AND we dont include risk factor in controls...infact we are trying to find an association of disease with risk factor in case control study....


Comparing exposure status in cases and control confounds the analysis.
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#18
Q 39 IN patients suffering from diseases of the lower motor neurone, grouping of muscle fibres of histochemical type 1 associated with a raised functional terminal innervation ratio has been demonstrated. This could be explained in either of two ways: (1) the neurones innervating type 2 muscle fibres are more susceptible to degeneration and when this occurs the denervated muscle fibres are re-innervated by collateral sprouts from nerve fibres previously innervating type 1 fibres. The type 2 fibres then take on the histochemical properties of type 1 fibres, which is in accordance with the demonstration2−4 that when a nerve previously serving a muscle containing predominantly type 1 fibres is transplanted into a muscle containing predominantly type 2 fibres, the histochemical characteristics of the latter become those of type 1 fibres. The mechanism by which this change comes about is uncertain, but it may be dependent on the frequency of passage of impulses along the nerve fibres5, a higher frequency favouring development of type 2 characteristics. The evidence against this explanation lies in the absence in most of our cases with type 1 grouping of any atrophic type 2 fibres. It is possible, however, that all the denervated fibres became re-innervated before they had time to atrophy. Further, where atrophic muscle fibres are present in primary disease of the lower motor neurone, in our experience (with human muscle) they are rarely predominantly type 2. (2) The re-innervating terminal sprouts, whether from axons of neurones previously serving muscle fibres of type 1 or 2, may be insufficiently mature to enable them to conduct every impulse reaching them from the parent axon. Thus the frequency of stimulation of the re-innervated muscle fibres would be substantially reduced. In these circumstances the type 2 muscle fibres, whether re-innervated by sprouts from axons previously serving type 1 or 2 fibres, would assume type 1 characteristics. Original type 1 fibres re-innervated in this way would, of course, retain their original histochemical characteristics irrespective of the type of muscle fibre previously—and still—innervated by the parent axon of the re-innervating sprou
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#19
39 D
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#20
just an fyi to everyone, here are my answers:

1. EBAAA
6. CEEFC
11. CBDBD
16. DCCEF
21. AACEC
26. EDEEB
31. CAADD
36. EBCDC
41. ADDCD
46. ADFBC
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