In de Clercq's edition, the text reads:
Leudegisilus diaconus in uicem.
Medardo presbytero.
Thus, de Clercq treats them as two separate entries and signatures, and seems to believe that Medardus was also present at the synod. Gaudemet follows this interpretation and translates Medardo Presbytero as "Médard, prêtre" (p. 505). Prosopographie Chrétienne suggests that Medardus attended the proceedings, but signed them through the help of Deacon Leudegisilus for unknown reasons (most probably Medardus was handicapé or illetré; see PCBE Gaule 2: Medardus 3). Hence, both de Clercq, Gaudemet, and PCBE claim that the synod was attended by 34 presbyters.
In my opinion, the most likely explanation is that Medardus was absent from the council, to which he sent as his representative one of his deacons, Leudegisilus. My argument is built on the following premises:
1. There is another deacon, Barbario, who signed the acts as a representative.
2. Canon 6 of this synod (see [1562]) decrees that in case of presbyter's sickness he should send a deacon to act in his stead.
3. Medardo presbytero is clearly in dative or ablative, and not in nominative. (Albeit, in vicem should be followed by genitive...)
4. Leudegisilus signed the acts for Medardus almost certainly because he was from the same parish. It seems, however, that only one person from a single parish attended the synod, or at least that only one person from the parish signed the acts. In my view, all deacons signing the decree act as the representatives of their respective parishes.