Proximal myotonic myopathy (PROMM) and other proximal myotonic syndromes

Late-Onset Proximal Myotonic Myopathy (PROMM): A Rare Presentation in an Adult

Proximal myotonic myopathy (PROMM) is normally associated with bilateral proximal weakness of lower limbs, slight elevation of liver enzymes, and cataracts. Myotonic dystrophy and PROMM are both autosomal dominant disorders, but gene study is completely normal in the case of PROMM. The most important differential diagnosis of PROMM is myotonic dystrophy. In our case, we reported late-onset PROMM in a patient 42 years old whose symptoms started at the age of 33 years; genetic evaluation of both myotonic dystrophy type 1 and myotonic dystrophy type 2 came out to be normal; therefore, the diagnosis of exclusion PROMM was made, which is a rare entity.

Early onset posterior subscapular cataract in a series of myotonic dystrophy type 2 patients

PurposeEarly onset posterior subscapular cataract (<50 years of age) is a characteristic feature of myotonic dystrophy type 2 (DM2). Nevertheless, despite being operated at a young age, many patients remain undiagnosed for years. The purpose of this study was to assess the prevalence of early onset posterior subscapular cataract as a presenting symptom of the disease in a cohort of patients with DM2.Patients and methodsWe retrospectively reviewed medical records of DM2 patients followed in our institution for the presence of early onset posterior subscapular cataract, of any secondary causes of cataract, of the age of onset of muscle weakness and of final disease diagnosis.ResultsTwenty-eight patients were studied. Nine patients (32.1%) had presented early onset posterior subscapular cataract at a median age of 43 years (IQR=36-46) and seven (25%) reported it was the presenting sign. No patient was referred for neuromuscular evaluation due to the occurrence of early onset cataract. Median delay between cataract onset and referral for neuromuscular evaluation was 10 years (IQR=6.0-19.5) and final DM2 diagnosis was achieved after a median of 16 years (IQR=6.5-19.5).ConclusionThis study shows that early onset posterior subscapular cataract was the first symptom of the disease in 25% of our DM2 patients. Nevertheless, none was suspected of having cataract in the context of DM2, and referral for neuromuscular evaluation was made after a long delay and usually following the appearance of other symptoms. Ophthalmologists can be the first physicians encountering these patients and should have a low threshold for referring them for neuromuscular evaluation.

Female patient with proximal myotonic myopathy and ventricular tachycardia

A 68-year-old woman with known proximal myotonic myopathy was transferred to our hospital for further diagnostic and therapeutic evaluation after successful termination of an episode of sustained ventricular tachycardia. In 2001, the myopathy was diagnosed after symptomatic weakness of the hip flexors. A cardiomyopathy with slight reduction of systolic left ventricular function was found in 2002. Coronary angiography excluded relevant coronary artery disease. The electrophysiologic examination could provoke atrial flutter, but neither a ventricular tachycardia nor a delay in the AV conduction was found. ECG and Holter ECG did not reveal any abnormalities. A reduction of the left ventricular systolic function (EF 45%) with normal size of cardiac chambers was demonstrated by echocardiography. It is known that in the patient group with myotonic dystrophies cardiac involvement manifests itself as cardiomyopathy, conduction disturbance or arrhythmia. However, only a small percentage of all patients with myotonic myopathy actually suffer from cardiac involvement. Among the different types of cardiac involvement, conduction disturbances requiring pacemaker implantation are most frequent. Only some patients develop ventricular tachycardias, and even cases of sudden cardiac death have been described. As a result of the case reports in the literature and the findings in our patient an ICD system was implanted on March 4, 2004.

Assessment of cardiovascular autonomic function in myotonic dystrophy type 2 (DM2/PROMM)

BACKGROUND

Proximal myotonic myopathy is an autosomal dominant multisystem disorder with a recently defined CCTG expansion on chromosome 3 in the major subgroup (myotonic dystrophy type 2). Cardiac rhythm disturbances have been described in patients with this disease, but it is not known whether myotonic dystrophy type 2/proximal myotonic myopathy patients suffer from dysautonomia and whether cardiac arrhythmias relate to autonomic dysfunction.

OBJECTIVES

To investigate cardiovascular autonomic function in myotonic dystrophy type 2/proximal myotonic myopathy patients with and without cardiac arrhythmias.

PATIENTS AND METHODS

Standard autonomic function tests (heart rate responses to Valsalva manoeuvre, deep breathing and active change of posture, and blood pressure responses to active change of posture and sustained handgrip), resting heart rate variability in the time- and frequency-domain, and the corrected QT interval length were determined in 16 patients with genetically defined myotonic dystrophy type 2/proximal myotonic myopathy and compared to the results obtained in 16 age- and sex-matched healthy control subjects.

RESULTS

Standard autonomic tests yielded similar results in both groups. Measures of heart rate variability tended to be lower in myotonic dystrophy type 2/proximal myotonic myopathy patients compared to healthy controls, but reached statistical significance only for the number of R-R intervals exceeding 50 ms (p50) and the power spectrum density in the low-frequency range (low-frequency power). Four patients (25%) suffered from mild cardiac rhythm disturbances encompassing paroxysmal tachycardia, sinoatrial block, right bundle branch block, ventricular premature beats and bradycardia. The autonomic responses of these patients were essentially similar compared to those without cardiac arrhythmias, apart from a decreased heart rate response to deep breathing in the patients with cardiac arrhythmias.

CONCLUSIONS

We found no major abnormalities of cardiovascular autonomic function in patients with myotonic dystrophy type 2/proximal myotonic myopathy, neither in the whole study group nor in the subgroup of patients with cardiac rhythm abnormalities.

Proximal myotonic myopathy: clinical and molecular investigation of a Norwegian family with PROMM

Proximal myotonic myopathy (PROMM) was first described in 1994 as a multisystem disorder with similarity to myotonic dystrophy (DM), but without the abnormal (CTG)n expansion in the DM protein kinase (DMPK) gene. The inheritance is autosomal dominant and the clinical features include myotonia, proximal muscle weakness and cataract. Linkage analysis in nine German PROMM families has indicated the possibility of linkage to DM2 locus on chromosome 3. We report a Norwegian PROMM family in which the proband was clinically diagnosed as DM but without the (CTG)n expansion. Using an intragenic marker we showed that the DMPK gene did not segregate with the disease in this family. All family members are heterozygous for the R894X mutation in CLCN1 gene. Linkage analysis could not be performed, but haplotyping probably excludes the DM2 locus as the disease locus in this family. The present family emphasises that myalgia is a prominent symptom in PROMM and the clinical differences may be explained by genetic heterogeneity. This family will be reinvestigated along with the identification of candidate genes or regions in larger PROMM families.