Distinct early symptoms in neuropathologically proven frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is associated with accumulation of neurodegeneration-related protein, such as tau, TAR DNA-binding protein 43 (TDP-43), or fused in sarcoma protein (FUS). There have been very few systematic studies of the early symptoms of clinical phenotypes: behavioral variant frontotemporal dementia (bvFTD), semantic variant primary progressive aphasia (svPPA). Clinical subtypes and the patterns of atrophy reflect protein-accumulation patterns, but the relationship between early symptoms and pathological findings remains unclear.

We retrospectively investigated the clinical records and examined the neuropathology of 39 bvFTD and 6 svPPA patients to identify symptoms appearing within 2 years of the first clinically apparent changes.

The bvFTD group consisted of 13 FTLD-tau, 18 FTLD-TDP, and 8 FTLD-FUS, and the svPPA group consisted of 6 FTLD-TDP. Age at death is significantly younger in FTLD-FUS (52.8 ± 12.6; P = 0.0104 < 0.05). Over 50% of bvFTD patients show apathy or inertia, and distinct language features appear early in svPPA. Interestingly, bvFTD and svPPA frequently present additional symptoms, not included in the diagnostic criteria, such as physical signs, reticence, dazed condition, and delusions. Stereotyped behaviors, hyperorality and dietary changes are prominent in FTLD-FUS, while linguistic deficits are greater in FTLD-TDP.

Specific symptoms tend to appear in the early stage of FTLD in each pathological background. They might reflect the morphological features and pathological progression, and should be helpful in the stratification of patients for future therapeutic trials based on the proteinopathies.