Xina, as I mentioned:
UMN damage is assessed by the clinical examination. Basically hyperreflexia (typically with spreading, i.e. the reflex can be elicited from a location nearby), spasticity, weakness, impared fine movements, loss of abdominal reflexes, positive Babinsky, clonus, increased jaw jerk (masseter reflex)..probably some more.
Trust me, UMN signs would not be missed during the exam. EMG would be clear.
If your clinical examination was clear, then you certainly do not have your descending motor pathways (UMN) involved.
UMN damage is not linked to LMN damage, both can exist independently as they are different structures. If only UMN is involved and there is no progression, the condition is called primary lateral sclerosis (because only the lateral columns - UMN - are involved). There are no LMN signs and hence no fasciculations.
Hope it helps with understanding and you can be reassured completely
