Respiratory Management of Myotonic Dystrophy

Patients with myotonic dystrophy can avoid episodes of respiratory failure by using up to continuous noninvasive ventilatory support (CNVS). Of 154 patients consecutively presenting to a neuromuscular disease clinic, 143 had types 1 or 2 and 11 had congenital myotonic dystrophy. Of the 76 who came multiple times, 41 were prescribed and used at least sleep NVS to relieve symptoms of fatigue and hypersomnolence. They had sleep and end-tidal (Pet) CO2 with highs over 50 mm Hg and many 4% or greater O2 desats per hour of sleep and all had mean sleep O2 sat levels less than 95% before beginning sleep NVS. Thirteen eventually had to extend NVS use into and eventually throughout daytime hours for CNVS. While using NVS during the day their arterial blood gases were within normal limits. When the 41 were using NVS only during sleep, 24 of the 41 also had normalization of diurnal SpO2 to ≥ 95% and decreased hypercapnia. The 41 patients have been using sleep NVS for 6.70±3.64 (range = 0.75 to 19) years per patient or for 274.7 patient-years. Seventy-two have died or been lost to follow-up. The 13 up to CNVS users have been doing so for 75.7 patient-years or a mean of 5.8±3.2 (range = 0.2 to 10) years per patient. The VC from ﬁ rst visit to most recent visit of all 71 decreased a mean 49.3±168.8 ml or about 1.5% per year. it decreased a mean 52±171 per year for the 41 NVS users over 274.7± 3.64 patient-years.

Support (NVS), they very often fail to use NVS suffi ciently either during daytime hours or overnight to maintain normal Arterial Blood Gases (ABGs). One study reported poor compliance with ventilator use by 62% of 38 patients by comparison with patients with other NMDs [4]. Thus, with many patients not benefi ting optimally from NVS, they can be hospitalized repeatedly before succumbing from cor pulmonale and cardiorespiratory failure.
Nevertheless, we suspect that those who do cooperate to use at least nocturnal NVS may have improved ABGs, symptoms, and survival [5]. It may be that the weaker patients, those wheelchair dependent with very low VCs, have better prognoses than ambulatory patients who do not appreciate the benefi ts of NVS and use it sparingly. Ambulatory hypercapnic myotonic dystrophy patients neither want to carry nor pull a ventilator with them while they walk nor do they feel so much benefi t as those in wheelchairs who literally can not breathe without up to continuous NVS [6,7].   (Table 1).

Discussion
The fact that nine myotonic dystrophy patients underwent Another study considered 12 patients using bi-level PAP.
Investigating the effects of a 1-month withdrawal followed by a 1-month reinstitution of bi-level PAP, settings not reported, initial diurnal PaCO2 43.1 mm Hg increased to 46.3 mm Hg after the one month withdrawal then decreased back to 43.9 mm Hg after one month of reinstitution; PaO2 83.6 mm Hg at baseline decreased to 76.9 mm Hg after one month withdrawal then increased to 80.9 mm Hg after one month of reinstitution.
Mean nocturnal O2 sat 95.0% at baseline decreased to 92.2% after one month withdrawal then increased to 95.1% after one month of reinstitution [9]. None of these studies described patients who, with time, became dependent on continuous ventilatory support. All our 13 patients using CNVS had normal CO2 and O2 sat levels while using it and the levels deteriorated and respiratory distress developed upon discontinuation of CNVS, including immediately for 8 patients.
A study of mortality in myotonic dystrophy over a 47 year period indicated a median survival of 60 years for males and 59 years for females with survival to age 65 only 18% by contrast to the normal 78%. The causes of death were about 30% from pneumonia and 30% from cardiac arrhythmias. Half of the patients were wheelchair-bound [10]. Inadequate ventilatory and cough assistance most probably played a big role in the deaths due to pneumonia, cor pulmonale, heart failure and fatal arrthythmias. These patients have periods when their CPF are very poor and they need access to MIE to avoid pneumonia.
Using NVS settings to normalize CO2 and O2 sat levels as well as AHI, rather than only low pressure support bi-level PAP, better improves blood gases and can prolong life by CNVS when needed. Some patients are being told that by polysomnography they have no evidence of sleep disordered breathing and do not require treatment despite severe hypercapnia that was not monitored but that we observed on presentation to us.
Apnea-hypopnea indices are often normal or normalized by noninvasive ventilation at less than NVS settings despite severe sleep hypercapnia that can result in cor pulmonale.
On conclusion, it is clear that occasional patients with myotonic dystrophy can become CNVS dependent, as an alternative to undergoing tracheotomy, and this can occur without hospitalization or an episode of acute respiratory failure.