According to a review of 61 studies of patients suffering from severel

A review of 61 people showed that for a large majority of the patients missing a night's sleep immediately lifted their depression.
Conventional treatments, which use drugs and electric shocks, often have serious side effects.

Still, sleep deprivation is not used to treat depression.

This is a paradox. We see that missing a night's sleep lifted depression. But this technique is not used to treat depression even though conventional methods to treat depression have serious side effects. Why? What explains that sleep depression is not used. We need a reason why it is not used. Could be because it has even more serious side effects or because it does not 'treat' depression and only leads to temporary effect etc or because it is not possible to keep people awake at regular intervals which is required for treatment etc

(A) For a small percentage of depressed patients, missing a night's sleep induces a temporary sense of euphoria.

We know that for most people missing a night's sleep lifts depression. For a small % of people, it induces temporary euphoria. It is a positive thing and hence, if anything, this makes a case for why sleep deprivation should be used. It doesn't explain why it is not used.

(B) Keeping depressed patients awake is more difficult than keeping awake people who are not depressed.

We don't know how difficult it is to keep those awake who are not depressed. What if it is easy to keep non depressed people awake but slightly harder to keep depressed people awake, but possible nonetheless? Since degree of difficulty is not mentioned, this is not correct. If we were told that it is extremely hard to keep depressed people awake, that would explain why this method is not used.

(C) Prolonged loss of sleep can lead to temporary impairment of judgement comparable to that induced by consuming several ounces of alcohol.

krndatta

This option is talking about the impact of 'prolonged loss of sleep'. Since 'prolonged' means for a long time, we would think that prolonged would likely be many days or weeks or months. The impact of something in a small amount or moderation could be very different from the impact of the same thing in extreme or in long term. Most things good for us, when taken in extreme, turn harmful. So how 'prolonged loss of sleep' impacts people is irrelevant.

(D) The dramatic shifts in mood connected with sleep and wakefulness have not been traced to particular changes in brain chemistry.

The point here is - how is brain chemistry linked to depression and its symptoms? Are changes in brain chemistry necessary to treat depression? If they have not been traced yet, does it mean they cannot be traced as per current knowledge? We don't know the answer to any fo these so irrelevant.

(E) Depression returns in full force as soon as the patient sleeps for even a few minutes.

We know that sleep is necessary. If depression will return as soon as the patient sleeps even for a short time, we cannot "treat" depression with sleep deprivation. If may give temporary relief but it will not treat it. Hence, it is not used to treat depression makes sense. This explains the paradox.

Answer (E)