Nope. There are tons of courses RPNs can take. RPNS are nurses too and they can specialize just like RNs. There are mental health , cardiac care, peri operative, palliative, foot care, OR, gerentology, wound care, antepartum, breastfeeding, orthopedics, diabetic ED, oncology, pediatric assessment, EKG, infection control, probably more.
Why would you think RPNs/LPNs can't specialize.