Following documentation from here:
https://www.visualstudio.com/en-us/docs/integrate/api/wit/work-items
AND
the object assembly here:
https://msdn.microsoft.com/en-us/library/microsoft.teamfoundation.workitemtracking.client.workitem(v=vs.120).aspx
[string]$TFSURI = $NMTFS_CollectionUri + "_apis/wit/workitems?ids=$itemNumber&fields=System.Id,System.Title,System.Description,System.History,System.AreaPath,System.TeamProject,"+`
"System.IterationPath,System.WorkItemType,System.State,System.Reason,System.CreatedDate,System.ChangedDate,System.ChangedBy,System.CreatedBy&api-version=1.0”
Code above does not yield all the fields speified, specifically missing Description and History objects, here is the results:
stem.Id : 612852
System.AreaPath : <myarea>
System.TeamProject : <myproject>
System.IterationPath : <myiteration>
System.WorkItemType : Task
System.State : To Do
System.Reason : New task
System.CreatedDate : 2017-01-12T15:34:19.06Z
System.CreatedBy : <MyName>
System.ChangedDate : 2017-01-12T16:39:23.35Z
System.ChangedBy : <MyName>
System.Title : test