Multi-system involvement characteristics and influencing factors of disease progression in Kennedy's disease.

Objective: To investigate multi-system involvement in Kennedy's disease and its association with disease progression. Methods: We retrospectively reviewed the clinical, laboratory, and electrophysiological data from 48 genetically confirmed patients with Kennedy's disease at the Department of Neurology, First Medical Center of the Chinese PLA General Hospital, between February 2016 and February 2024. The disease progression rate was calculated based on the functional scores at baseline and follow-up. Correlation analyses and multiple linear regression models were employed to assess the relationships among clinical variables and to identify potential predictors of disease progression. Results: The age of muscle weakness onset ranged from 16 to 66 years (mean 42±11 years), with a diagnostic delay of 5.0 (3.0, 9.8) years. Lower limb weakness was the most common initial symptom in 72.9% (35/48) of patients, and 37.5% (18/48) exhibited non-motor manifestations prior to the onset of weakness. Core motor manifestations included bulbar weakness (89.6%, 43/48) and symmetric proximal limb weakness (83.3%, 40/48), frequently accompanied by gynecomastia (74.2%, 23/31) and sexual dysfunction (64.6%, 31/48). The median CAG repeat length was 43 (42, 46), which showed a significant negative correlation with the age at onset (r=-0.406, P=0.004). Patients with CAG repeats > 43 had a higher prevalence of sexual dysfunction. Elevated serum muscle enzymes were observed in 97.9% (47/48), and abnormal sex hormone levels were detected in 81.2% (39/48). Sensory neuropathy was present in 68.1% (32/47), with CAG repeat length inversely correlating with compound muscle action potential (CMAP) amplitudes in the median (β=-0.29; t=-2.27, P=0.029) and ulnar (β=-0.22; t=-2.23, P=0.031) nerves. Low-frequency repetitive nerve stimulation (RNS) revealed a decrement in 43.3% (13/30) of patients, most commonly affecting the axillary and spinal accessory nerves. The disease progression rate was 1.3±0.3 (range: 0.5-2.0). Furthermore, serum creatine kinase-MB (CK-MB) levels were negatively correlated with disease progression rate (r=-0.303, P=0.036). Conclusions: Kennedy's disease presents with diverse initial manifestations and frequent multi-system involvement. Non-motor manifestations may precede muscle weakness, serving as valuable clues for early diagnosis. Widespread sex hormone abnormalities (particularly testosterone/luteinizing hormone dysregulation) support the role of androgen insensitivity in disease pathogenesis. Sensory neuropathies are frequent and not length-dependent. The presence of decremental responses on low-frequency RNS suggests neuromuscular junction dysfunction, which may underlie motor impairment in patients with Kennedy's disease. Finally, serum CK-MB may serve as a potential biomarker for disease progression.