SOME FOLKS have lice; some have fleas. Others have lice and fleas. Some even have lice, fleas, and scabies. It depends on how hard one looks for the little devils. Some living conditions predispose to picking up all of these little creatures.
Although parsimony is a virtue, and medical students have always been urged to seek a single unifying diagnosis, in fact, many patients have more than 1 thing wrong with them. Individuals seem to accumulate diseases (and polypharmacy) as they age. Geriatricians are well aware that multiple coexisting diagnoses are the rule, not the exception.
Caplan LR. Lice, Fleas, and Strokes. Arch Neurol. 2000;57(8):1113-1114. doi:10.1001/archneur.57.8.1113