in 2011, the classification of primary progressive aphasia was updated to include three clinical variants. patients must first be diagnosed with ppa, and then divided into variants based on speech production features, repetition, single- word and syntax comprehension, confrontation naming, semantic knowledge, and reading/spelling. in the classical mesulam criteria for primary progressive aphasia, there are two variants: a non-fluent type progressive nonfluent aphasia (pnfa) and a fluent type semantic dementia (sd). a third variant of primary progressive aphasia, logopenic progressive aphasia (lpa) was then added, and is an atypical form of alzheimer's disease. for pnfa, the core criteria for diagnosis includes agrammatism and slow, and labored speech. inconsistent speech sound errors are also very common, including distortions, deletions, and insertions. in terms of comprehension, there are deficits in syntax and sentence comprehension due to grammatical complexity, but single- word and object comprehension is relatively maintained. the second variant, sd, presents with deficits in single-word and object comprehension. naming impairments can be severe, specially for low-frequency objects, and can eventually lead to a more widespread semantic memory deficiency over time. the ability to read and write can also be impaired if there are irregularities between pronunciation and spelling. however, repetition and motor speech is relatively preserved. the logopenic variant involves impairments in word retrieval, sentence repetition, and phonological paraphasias, comparable to conduction aphasia. compared to the semantic variant, single word comprehension and naming is spared, however, sentence comprehension presents difficulty because of length and grammatical complexity. speech will include incomplete words, hesitations preceding content words, and repetition. however, these ppa subtypes differ from similar aphasias, as these subtypes do not occur acutely following trauma to the brain, such as following a stroke, due to differing functional and structural neuroanatomical patterns of involvement and the progressive nature of the disease.