Myotonic dystrophy type 2 (DM2)

Overview

Myotonic dystrophy type 2 (DM2), also known as proximal myotonic myopathy (PROMM), is closely related to DM1 but generally milder and, notably, has no congenital (from-birth) form. It causes progressive weakness and wasting affecting skeletal muscle, the heart, lungs and digestive system, and is less common than DM1.

Symptoms

Weakness usually centres on the thighs, hips and upper arms, making stairs, standing and lifting harder, and affecting balance too. Muscle pain — aching or cramping — is common, varies day to day, and can be worsened by weakness, fatigue or certain medications (statins among them); pain more broadly can affect muscles, joints, the spine and ligaments, especially in the neck, back, shoulders, hips and thighs. Myotonia (difficulty relaxing muscles after use) mainly affects the hands and jaw and eases with repeated movement. Unlike DM1, facial weakness is usually mild or absent.

Heart rhythm problems can occur, making regular check-ups worthwhile. Breathing can be affected, particularly overnight, contributing to excessive daytime sleepiness and, in some, respiratory insufficiency; a weaker cough raises the risk of chest infections and aspiration pneumonia. Gut symptoms — slow digestion, constipation, diarrhoea, bloating — and swallowing difficulty (which can cause weight loss) are both common. Endocrine effects include higher rates of diabetes, an underactive thyroid, adrenal insufficiency and fertility problems. Early cataracts, squints, drooping eyelids and dry eyes can occur, as in DM1, and cognition is generally less affected than in DM1, though concentration, memory, decision-making and mood can still be affected in some people.

Inheritance

DM2 is autosomal dominant — one changed copy from a parent is enough — caused by an abnormally long repeated DNA sequence (a CCTG repeat) in the CNBP gene on chromosome 3. Unlike DM1, DM2 doesn't show 'anticipation' (worsening across generations): fewer than 28 repeats is normal, 28–75 may or may not cause symptoms, and more than 75 typically does.

Getting a diagnosis

A GP refers to a neurologist, who bases the initial diagnosis on symptoms, examination and family history, then confirms it with a genetic blood test for the CCTG repeat in the CNBP gene.

Management and outlook

Care is multidisciplinary. Annual ECGs help catch heart rhythm problems early, with ablation, a pacemaker or an implantable defibrillator used if needed. Breathing is monitored with lung function tests and sleep studies, with non-invasive ventilation and cough-assist devices as needed; modafinil may be considered for excessive daytime sleepiness, and annual pneumococcal, flu and COVID-19 vaccines are recommended.

Physiotherapy — stretching, strengthening, low-impact aerobic exercise, orthotic support — helps maintain function; pain is generally managed with NSAIDs, with opioids used cautiously given the respiratory risks. Speech and language therapy supports swallowing, with dietitian input for nutrition and gut symptoms (a high-fibre diet, more fluids, medication, or further investigation if severe). An endocrinologist can help manage the metabolic effects, and annual eye checks watch for cataracts. Before any surgery, the anaesthetic team needs to know about the diagnosis and any heart or breathing issues well in advance.