Proposed Guidance for DMD-Related Respiratory Function Evaluation in the UK

Proposed guidance on managing day-to-day and acute respiratory care in Duchenne muscular dystrophy (DMD) for adult and pediatric patients covers assessment, monitoring, and emergency management, with backing from the British Thoracic Society (BTS).

The multidisciplinary team who proposes these recommendations consists of 2 BTS representatives, 2 patient representatives, 3 neuromuscular clinicians, and 4 respiratory specialist physiotherapists; together they make up the Respiratory Care Working Group of DMD Care UK. Publishing their findings in Thorax, they note that inconsistent respiratory care in the DMD setting necessitates this guidance for public health care systems.¹

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“Respiratory complications are a major cause of morbidity, unplanned hospital admission, and remain the second most frequent cause of death in DMD, after cardiac failure,” the team wrote. “Maintaining respiratory health is vital to prolonging survival and quality of life in DMD.”

Of foremost importance is regular surveillance of respiratory function, keeping in mind that respiratory weakness from DMD is inevitable and parallels weakness in upper limb function. The threshold for referral to pulmonary function testing should be lower, and referral to a specialist takes place during pediatric care. Per the authors, 4 years is the average age of DMD diagnosis in the United Kingdom, while previous research also suggests diagnosis around age 5 years in the United States and Europe.²

Routine monitoring and assessment should include monitoring respiratory function every 6 months on an ongoing basis but more frequently per symptom severity, accurate and regular height measurements for valid forced vital capacity (FVC) predictions, and evaluating for potential symptoms of sleep-disordered breathing, with extra attention paid to patients classified as overweight or who have Cushingoid features. In addition, there should be careful scrutinization of prescribing drugs that suppress respiratory function in any patient with an FVC below 80%.

Overall triggers for respiratory evaluation should encompass any symptom of disordered breathing; inability to complete spirometry, significant scoliosis, and/or a Brooke scale score of 3 or more; FVC percentages below 30% or of 50% and below per age and height values; and recorded decline in peak cough flow.

Emergency plans are also a necessity in acute care settings and instances of rapid patient deterioration, particularly because signs of respiratory distress may not fit be obvious or expected, the authors write. When stabilization is necessary following an emergency department admission, there should be mandatory medical and physiotherapy reviews. It’s vital at this point to have contact with a respiratory specialist or to consider transfer to specialized care should a specialist be unavailable, they emphasize.

Emergency dosing of hydrocortisone is a noted option among patients with DMD with severe illness, especially since long-term steroid use—meant to improve muscle strength and function³—can lead to adrenal suppression.

Regarding ventilatory support, the team’s proposed guidance advises against administering oxygen because doing so can hasten disease worsening or respiratory failure. However, noninvasive ventilation (NIV) should be a first-line treatment consideration. Tracheostomy and acute ventilatory support should only be performed under the guise of a specialist respiratory unit, center, or with a team experienced in DMD management, and ventilatory support “is the preferred method for managing respiratory failure.”

In instances of hypoxemia, the authors say to monitor CO2 levels, have low thresholds for arterial blood gas analysis and critical care, and offer first-line NIV in instances of hypercapnia. Also important is to avoid high-flow oxygen but provide supplemental oxygen in place of ventilation for pediatric patients with a saturation below 92% and adult patients with a saturation below 88%.

Additional considerations are contributions from fat embolism and dilated cardiopmyopathy, which the authors note should always be considered in the settings of acute respiratory symptoms and rapid deterioration and when first developing respiratory symptoms, respectively.

“The guidelines highlight the importance of multiple factors, clinical experience and judgement, and patient/family circumstance in supporting optimal routine and emergency respiratory care for individual patients,” the team concludes. “DMD remains a rare disease and therefore increased awareness of the condition and its implication is critical.”

References

1. Childs AM, Turner C, Astin R, et al. Development of respiratory care guidelines for Duchenne muscular dystrophy in the UK: key recommendations for clinical practice. Thorax. Published online December 20, 2023. doi:10.1136/thorax-2023-220811
2. Wong SH, McClaren BJ, Archibald AD, et al. A mixed methods study of age at diagnosis and diagnostic odyssey for Duchenne muscular dystrophy. Eur J Hum Genet. 2015;23(10):1294-1300. doi:10.1038/ejhg.2014.301
3. Torgan C. Optimizing steroid treatment for Duchenne muscular dystrophy. National Institute of Arthritis and Musculoskeletal and Skin Diseases. March 8, 2018. Accessed January 2, 2024. http://tinyurl.com/55b3ej2n