Question of the day #2 (Hearing Loss)

[Haisook]

Ok, here's a question that I've written.

A 35 year old Caucasian woman who works in a confectionery factory presents with complaints of hearing loss in both ears. She has no other complaints. Microscopic examination shows undamaged, but defective hair cells in the inner ear. Which of the following is most likely responsible?

A. Increased volume of endolymph
B. Increased pressure in the scala media
C. Pressure on the vestibulocochlear nerve
D. Structural defect in a protein
E. Lesion in the cochlear nucleus
F. Noise pollution

You should attach an explanation to your choice as well...

[step1an]

D. Structural defect in a protein

[Shade Grown]

F. Noise Pollution!

[donofitaly]

F. Noise pollution due to her job profile.

[ashishkabir]

Yup - Noise pollution: Continuous exposure to loud noise also can damage the structure of hair cells, resulting in hearing loss and tinnitus

http://www.nidcd.nih.gov/health/hearing/noise.asp

[drsue]

F. Noise pollution

[awakened]

F. noise pollution ....increased noise for long durations can cause rise in the thresholds of sound audible for a person

[Haisook]

Well, alas, only step1an is correct!!

Correct answer is:
D. Structural defect in a protein

The question stem mentions "undamaged, defective hair cells". Hair cells are a modified type of microvilli, called stereocilia. They have the basic structure of microvilli; microfilaments (composed of a protein, actin), covered by a glycocalyx. Actin is responsible for the movement of those structures. A structural defect in actin can cause undamaged, normal-numbered, but defective hair cells.

A. Increased volume of endolymph & B. Increased pressure in the scala media: these are the hallmarks of Meniere disease. There's deficient absorption of endolymph, leading to its accumulation in scala media. By pressure effects, hair cells get damaged. The classic presentation is episodic SNHL, tinnitus, and vertigo.

C. Pressure on the vestibulocochlear nerve: would not cause defective hair cells, and moreover is unlikely to be bilateral except in the case of bilateral schwannomas which is only likely in a patient with neurofibromatosis 2.

E. Lesion in the cochlear nucleus: would not cause defective hear cells, and it causes a unilateral SNHL.

F. Noise pollution: this has been the answer most of you have chosen, but it's incorrect, because noise pollution, though can cause bilateral SNHL, does damage the hair cells directly, leading to loss of hair cells which cannot grow back. Signs of damage and hair cell loss are evident on microscopy. The question stem explicitly mentions that the hair cells examined were undamaged. The patient's job in a confectionery factory is a distractor!

[ashishkabir]

Originally Posted by Haisook

Well, alas, only step1an is correct!!

Correct answer is:
D. Structural defect in a protein

The question stem mentions "undamaged, defective hair cells". Hair cells are a modified type of microvilli, called stereocilia. They have the basic structure of microvilli; microfilaments (composed of a protein, actin), covered by a glycocalyx. Actin is responsible for the movement of those structures. A structural defect in actin can cause undamaged, normal-numbered, but defective hair cells.

A. Increased volume of endolymph & B. Increased pressure in the scala media: these are the hallmarks of Meniere disease. There's deficient absorption of endolymph, leading to its accumulation in scala media. By pressure effects, hair cells get damaged. The classic presentation is episodic SNHL, tinnitus, and vertigo.

C. Pressure on the vestibulocochlear nerve: would not cause defective hair cells, and moreover is unlikely to be bilateral except in the case of bilateral schwannomas which is only likely in a patient with neurofibromatosis 2.

E. Lesion in the cochlear nucleus: would not cause defective hear cells, and it causes a unilateral SNHL.

F. Noise pollution: this has been the answer most of you have chosen, but it's incorrect, because noise pollution, though can cause bilateral SNHL, does damage the hair cells directly, leading to loss of hair cells which cannot grow back. Signs of damage and hair cell loss are evident on microscopy. The question stem explicitly mentions that the hair cells examined were undamaged. The patient's job in a confectionery factory is a distractor!

You know, I thought that was the answer, because even my explanation states "can damage hair cells" and the question stem said undamaged. However, the woman is 35 - how did actin acquire a bilateral defect (implying that something was fundamentally wrong with either the gene for the protein or with the processing of the protein) *only* in the ears after all these years? So thats why I went with the lesser of 2 evils and chose the damage option anyway.

[Haisook]

You're correct. May be the case is not possible in reality, but I've seen worse questions on UW! I noticed that the case must not always be of actual clinical significance, and many times the cases are of pure theoretical interest.

That's why I've written such question. Another reason is to emphasize 2 points:

1. Hair cells are stereocilia, a form of microvilli, not cilia.
2. Noise pollution produces mechanical damage to the hair cells.

[ashishkabir]

Originally Posted by Haisook

You're correct. May be the case is not possible in reality, but I've seen worse questions on UW! I noticed that the case must not always be of actual clinical significance, and many times the cases are of pure theoretical interest.

That's why I've written such question. Another reason is to emphasize 2 points:

1. Hair cells are stereocilia, a form of microvilli, not cilia.
2. Noise pollution produces mechanical damage to the hair cells.

Yup - UW and I disagree like this all the time... Thanks for the Q...

[drarnab]

Originally Posted by Haisook

You're correct. May be the case is not possible in reality, but I've seen worse questions on UW! I noticed that the case must not always be of actual clinical significance, and many times the cases are of pure theoretical interest.

That's why I've written such question. Another reason is to emphasize 2 points:

1. Hair cells are stereocilia, a form of microvilli, not cilia.
2. Noise pollution produces mechanical damage to the hair cells.

Thanks for the interesting question. I would have gone with structural defect of the protein too. But im slightly worried as microfilament defects might be incompatible with life not just sterocilia..... obviously that would mean saying bye bye to your intestinal microvili as well...

As for case presentations, I thought id mention that the NBME requires all questions to be written "in accordance with the accepted epidemiology for the condition (if it exists of course)".