Poor Neck Proprioception May Cause Balance Deficits in Myotonic Dystrophy 1

Poor Neck Proprioception May Cause Balance Deficits in Myotonic Dystrophy 1

Impairment of balance and gait are frequent complaints in patients with myotonic dystrophy type 1 (DM1). In these persons, there is an increased risk for stumbles and falls when compared to normal subjects. An underestimated cause of falls might be the weakness of neck flexor muscles (due to cervical ataxia). It is well known that fibres of muscle spindles are receptors combining a specialized sub-set of muscle fibers with a specialized array of both sensory and motor nerve fibers. Spindles transduce into neural afferent discharges the muscle length and length changes. They are very dense in deep neck muscles, are crucial to body balance and gage orientation, and are severely affected in DM1. Preliminary results suggest that falls could reflect imbalance. These indicate that cervical ataxia may come into play because of muscle spindle fibre disruption. In light of the current knowledge on the physiology of balance and on the association between balance deficits and cervical dystonia in other clinical conditions (e.g., whiplash injury), a rationale is therefore offered to a confirmation of the hypothesis that DM1 patients may suffer from cervical ataxia.

The primary endpoint is the demonstration of an association between balance deficits in standing and cervical proprioception deficit in adults affected by Myotonic dystrophy 1.

Secondary endpoints are:

• the investigation of the correlation among the two deficits and the clinical conditions of patients,
• the definition of normative data in the measure of cervical proprioception in a sample of healthy participants.

It is expected that high scores in postural balance, obtained on the posturographic Equitest™-Sensory Organization Test-SOT, correspond to high levels of repositioning accuracy in tests of cervical repositioning and low SOT scores correspond to low accuracy. Moreover, it is expected that an association exists among the two deficits and the clinical situation of the patients. Results from the present pilot study will allow an estimate of the sample size for future experimental protocols. The evidence for an association between balance deficits and cervical ataxia would be of obvious relevance to the patients. This would also support the hypothesis that neck muscle spindles may be especially affected in DM1. This would highlight that muscles are also crucial sensory organs, involved in the perception of joint position, muscle strength, and fatigue. Results from the present study might allow the definition of new rehabilitative programs, such as treatments through a neck strengthening (and thus stiffening) exercise program. This study, therefore, might stimulate new research hypothesis at the neurophysiologic level and possibly lead to findings generalizable from DM1 to other forms of myopathy.

Inclusion Criteria:

• Diagnosis of DM1 since at least 5 years;
• Ability to stand erect with open eyes for at least 20 s;
• Rivermead Mobility Index (RMI) score ≥ 10/15;
• Visual acuity > 10/20, also with corrective lenses;
• Mini Mental State Examination (MMSE) score ≥ 26/30;
• ability to wittingly sign the informed consent form.

Exclusion Criteria:

• neurological or orthopedic pathologies with impact on balance;
• pregnancy;
• previous orthopedic surgical intervention;
• head or neck trauma in the 6 months preceding the study;
• other pathological conditions which could alter balance;
• drug therapy, underway for less than one month before the study, with impact on balance.