Courtesy of bostonherald.com:
It appears he is being suspended for violation of the league's banned substances policy, but there is currently no confirmation of what the substance was.
The rookie Spikes has 61 combined tackles, 3 pass defenses, and one interception this season. The interception came in the Patriots most recent game against the Jets.
A second round pick, he is a player that has started 8 games this season. He hopes to return for the playoffs.
UPDATE: Per Spikes' statement:
The substance was a medication that I should have gotten clarification on before taking.