Yes, it is possible to take an HSA distribution for medical expenses without limiting your ability to deduct medical expenses incurred this year. USC 26 Sec. 223(f)(6):
For purposes of determining the amount of the deduction under section 213 [Note: the provision of the Internal Revenue Code governing the medical expense deduction], any payment or distribution out of a health savings account for qualified medical expenses shall not be treated as an expense paid for medical care.
Thus, you can deduct any deductible medical expenses up to the point that it is paid for by your HSA--then it is deemed no longer a deductible medical expense. So if you take a distribution from your HSA, but you only use those funds to pay for prior-year, undeducted medical expenses, the current-year medical expenses remain deductible.
This is backed up by IRS Pub 696:
You must keep records sufficient to show that:
The distributions were exclusively to pay or reimburse
qualified medical expenses,
The qualified medical expenses hadn’t been previously
paid or reimbursed from another source, and
The medical expenses hadn’t been taken as an itemized deduction in any year.
Reading between the lines, the HSA distribution is not taxable income if they are a) for medical expenses, b) haven't been paid for before, and c) weren't deducted before. That is very much not the same as "a distribution is not a distribution if you are taking the medical expenses deduction".
Likewise, Pub. 502 reads:
Health Savings Accounts
You can't include in medical expenses any payment or
distribution for medical expenses out of a health savings
account.
which is very different from "you cannot take this deduction if paying for any medical expenses from an HSA."
