PERIPHERAL NEUROPATHY IN MYOTONIC DYSTROPHY TYPE 1

Abstract

Myotonic dystrophy 1 (DM1) is the most common muscular dystrophy in adult life characterized by a wide range of clinical features. The presence of peripheral nerve involvement has been debated. Previous studies have been limited by their small sample size and various definitions of peripheral neuropathy. Furthermore, the consequences of any possible neuropathy are unknown. Our aim was to verify the presence of polyneuropathy (PNP) in a large cohort of DM1 patients and to determine its clinical relevance. 94 DM1 patients (54 males and 40 females) underwent a structured neurological examination, including assessment of muscle strength, deep tendon reflexes and sensory modalities. Peripheral motor and sensory nerve conduction studies were performed in all patients. PNP was diagnosed if distal motor latency or conduction velocities were abnormal in at least two motor nerves or one sensory nerve. In addition, balance impairment was assessed with the Berg Balance Scale and physical and mental health status were evaluated with the SF-36 Health Survey. Patients with other conditions known to cause PNP were excluded from the study. PNP was present in 17 patients (18%). Age, sex and duration of neuromuscular symptoms were not associated with PNP. However, muscular strength was significantly lower in patients with PNP than in those without (p=0.008). In particular, distal muscle strength was more impaired (p=0.004). An absence of Achilles-tendon reflexes was more common in the group with PNP (p=0.013). Pinprick, light touch and joint position sense were normal in all patients. Vibration sense was reduced in only one patient with peripheral nerve involvement. The presence of PNP had no influence on balance impairment, mental health or physical health scores of DM1 patients. In general, the SF-36 Health Survey indicated that DM1 patients were significantly impaired regarding physical health but not mental health compared to the Dutch population. We found axonal PNP in 18% of DM1 patients. PNP was significantly associated with decreased distal muscle strength and absence of Achilles-tendon reflexes. However, the presence of PNP has no significant effect on balance impairment, mental and physical health.