Left untreated, Lyme disease can cause: 1  Chronic joint inflammation (Lyme arthritis), particularly of the knee. 2  Neurological symptoms, such as facial palsy and neuropathy. 3  Cognitive defects, such as impaired memory.4  Heart rhythm irregularities. 5  Risk factors.6  Preparing for your appointment.eft untreated, Lyme disease can cause: 1  Chronic joint inflammation (Lyme arthritis), particularly of the knee. 2  Neurological symptoms, such as facial palsy and neuropathy. 3  Cognitive defects, such as impaired memory.