Sequential dependent markdown parameters

Question

I would like to create a parameterized markdown document with two parameters where available options for the second input are dependent on the first. In my case I am dealing with a database of patients and visit dates, so the first input would be the patient ID, then code with generate a list of dates for that patient and the second input would be the index of the available. So something like:

---
title: "Dependent Inputs"
output: html_document
params: 
  MRN: "Medical Record in Database to Assess"
  D_idx: "The Date index from list for this subject"
---

# First get MRN:
params$MRN

# After user input MRN then filter and list possible dates
DB %>% filter(ID == MRN)  %>% select(Dates)

# Now enter date index for this MRN
params#D_idx

# Do the rest of the analysis using MRN and Date to get desired dataset ...

The interaction between the two doesn't seem possible. Tried using some shiny widgets as well but I am only interested in getting the user input to run the rest of the script, not rendering shiny outputs.