In looking for the information about the elevators at Abbesses and Lamarck-Caulaincourt, I came across this information that will be of interest for travelers to Paris: the platforms of the metro line 4 at the Chatelet station will be closed beginning next Monday through March 7, 2018.
What does this mean? You will not be able transfer to or from a line 4 train at Chatelet station (nor will you be able to catch a line 4 train there or descend from one). Line 4 trains will continue to go through the station, but without stopping.
You can go to catch the line 4 at Cité station (600 meters away) or Les Halles (450 meters away).
If you're on the 4 and need to transfer to RER A, RER B, or RER D, the website advises you to change at Les Halles.
Basically this means no easy changes from the 1 Line (east-west) to the 4 line (north-south) for the period of the construction.