Pleading the 5th

In light of recent "situations" involving cpunks and the courts, I've been thinking about the 5th Amendment. I pose two questions: If called to testify in a criminal case, and asked the question "Are you known by any other names" (or a derivative of that question), could one plead the fifth in order to prevent the disclosure of a pseudonym? If asked the question "have you ever communicated with [third party]", could one plead the fifth if that communication was made through a pseudonym, and tying that pseudonym to oneself could potentially be incriminating?