A Test to see whether its Telogen Effluvium....
As suggested by someone else on this forum, just take a sheet of white paper and rub your head vigorously until some hairs fall on it. Then examine the hairs. If they are mostly thick terminal hairs with only slight variation in diameter and length , then its Telogen Effluvium. If there are many weak, thin hairs of intermediate length, then its most likely. Remember, a FEW vellus hairs exist in the scalp of all people, even those with no male pattern baldness. The ratio of vellus to terminal (normal thick) hairs in non-male pattern baldness people is on average , 1:7. A significantly greater ratio suggests male pattern baldness.
Although your case is **** likely **** to be Telogen Effluvium, thinning on the sides and back is not always Telogen Effluvium-related. Don't get scared by what I am about to tell you, this is a VERY rare condition and afflicts only the most unfortunate people. I highly doubt that you have it. It is just for your information.
There is one variant of male pattern baldness (the WORST variant which puts even regular NW7s to shame) which is called Diffuse Unpatterned Alopecia (DUPA for short). This variety involves severe, often rapid miniaturization (thinning) of the ENTIRE scalp, including the sides and back, without passing through the regular Norwood stages. It eventuates in a horseshoe resembling that of a typical NW7, but with one major difference: It looks almost "transparent" due to the extensive thinning within the horseshoe zone. In other words, people with DUPA inevitably end up with extensive hair loss without a stable "permanent" zone and therefore cannot have a transplant. And yes, this condition is real, although rare : I have seen three such people so far. It is just pitiful. Not only is there no hair on the top of the head, but the sides and back have practically disappeared with only a few wispy hairs remaining to indicate the "shadow" of where hair once was. I don't wish this upon anyone, not even my worst enemies.
As for your Telogen Effluvium, once you are sure that it is indeed Telogen Effluvium (after getting a proper diagnosis), ask your derm what to do about it.
Cheers,
Arjun