Fading Muscle and a Flaccid Bladder: Atonic Bladder in a Case of Myotonic Dystrophy—A Case Report

Abstract

Background

Myotonic dystrophy Type 1 (DM1) is a multisystem genetic disorder characterised by progressive muscle weakness along with ocular, cardiac and endocrine abnormalities. However, detrusor underactivity manifesting as urinary retention is an under-recognised and rarely reported complication.

Purpose

To highlight a case of urinary retention caused by detrusor muscle underactivity in a young female with classic features of DM1, highlighting the need for early recognition and management of this rare but significant manifestation.

Methods

This case is of a 31-year-old female with urinary retention due to detrusor muscle underactivity, which is an under-recognised complication of DM1. The patient had classical features including grip myotonia, frontal balding, ptosis, intellectual impairment and early cataract changes. Uroflowmetry and significant post-void residual volume confirmed an atonic bladder. Elevated creatinine phosphokinase levels prompted electromyography, which demonstrated myotonic dive bomber discharges, and genetic testing identified pathogenic CTG trinucleotide repeat expansion in the myotonic dystrophy protein kinase (DMPK) gene.

Result

The patient was treated initially with clean intermittent catheterisation and Bethanechol (muscarinic agonist), then switched to indwelling urinary catheterisation due to improper technique. However, the risk of recurrent urinary tract infections remains a concern. Carbamazepine improved grip myotonia.

Conclusion

This case highlights the importance of the recognition of urinary retention as an important complication of DM1 and early recognition and treatment to prevent complications like recurrent urinary tract infections.

Introduction

Myotonic dystrophy Type 1 (DM1) is a neuromuscular illness that affects multiple systems, caused by an abnormal expansion of CTG trinucleotide repeats in the myotonic dystrophy protein kinase (DMPK) gene located on chromosome 19. ¹ It is characterised by progressive muscle weakness, myotonia, fatigue and cognitive deficits. ² The clinical spectrum of DM1 is extensive, exhibiting diverse symptoms dependent upon the age of onset. Mild variants are linked to cataracts and mild myotonia, resulting in near-normal life expectancy. ³ The typical adult manifestation is characterised by muscle atrophy, myotonia, cataracts and cardiac conduction abnormalities, often resulting in disability and diminished longevity. ⁴ Congenital DM1 is the most severe form, distinguished by hypotonia, respiratory failure at birth and substantial intellectual disability; early mortality is common. ⁵ Various systems of classification exist; however, Antonio et al. proposed a five-phenotype model delineated by age of onset: congenital, infantile, juvenile, adult, and late-onset. ⁶ However, significant inter-individual variability among symptoms and disease progression exists within these categories. ⁷

Urinary incontinence is prevalent in the general population, affecting an estimated 30%–60% of middle-aged and elderly women and 11%–34% of older males. The prevalence of this condition among postpartum women who are younger ranges from 15% to 30%.^{8, 9} Symptoms of lower urinary tract dysfunction, such as detrusor underactivity, poor bladder emptying and more significant post-void residual volumes, have been documented in DM1. ¹⁰ These signs may lead to urine retention, recurrent urinary tract infections and progressive renal impairment, thereby dramatically diminishing quality of life. ¹¹ The existing literature on bladder involvement in DM1 mainly comprises limited case series and observational studies, which restrict accurate prevalence estimation. Recognizing these complications is essential for timely diagnosis and appropriate management. ¹²

Case Report

Medical History

A 31-year-old unmarried female presented with progressive difficulty in climbing stairs for five years, had a history of sporadic urinary retention for three years, and a recent onset of hand grip weakness for six months. She also reported a fall one week prior to admission. She was born of a third-degree consanguineous marriage and had a history of delayed motor and speech milestones; however, she has since achieved good catch-up in both domains. She was diagnosed with Type 2 diabetes mellitus three years ago and has been on oral hypoglycaemic agents. She had also undergone right ovarian cystectomy for an ovarian cyst torsion 13 years ago. She has had a history of irregular menses and has been amenorrhoeic for the last three years.

Clinical Examination

On general examination, the patient was moderately built with bitemporal hollowing, bilateral ptosis, frontal balding and hypothenar muscle wasting, giving a characteristic hatchet facies (Figure 1). Her vital signs were stable. Grip myotonia was present. Pallor was present.

Figure 1.

Bitemporal Hollowing, Frontal Balding, Characteristic Hatchet Facies.

Neurological examination revealed proximal and distal muscle weakness with Medical Research Council (MRC) grade 3/5 power in both shoulder joints and wrists, and 4/5 power in elbows and lower limbs. Hypotonia was present in all four limbs. Deep tendon reflexes were diminished (1+) across upper and lower limbs, and the plantar reflex was flexor on the right and equivocal on the left. Superficial reflexes were intact. Cranial nerve and sensory examinations were normal. Cerebellar signs, including finger-nose testing, dysdiadochokinesia and rebound phenomenon, were absent.

Evaluation

Baseline investigations of the patient are summarised in Table 1. Ultrasonography revealed a post-void residual urine volume of 1.2 litres along with bilateral moderate hydroureteronephrosis. Uroflowmetry demonstrated a poor flow pattern with a prolonged time to maximum flow (21.6 seconds), a maximum flow rate (Qmax) of 8.3 mL/sec, and an average flow rate (Qavg) of 6.4 mL/sec—findings suggestive of detrusor underactivity (Figure 2). Electrocardiography (ECG) showed a left anterior fascicular block. Ophthalmological evaluation revealed bilateral early cataract changes. Neuropsychological assessment using the Binet Kamat test indicated moderate deficits in intellectual functioning. MRI spine revealed diffuse disc bulge with posterior annular tear at L4-51 and L5-S1 level, causing spinal canal stenosis with crowding of cauda equina nerve roots, bilateral neural foraminal narrowing, abutting the bilateral traversing nerve root. Nerve conduction studies showed bilateral axonal neuropathy involving the common peroneal and tibial nerves. Electromyography of the bilateral deltoid and right biceps muscles demonstrated spontaneous myotonic discharges resembling ‘dive bomber’ patterns (Figure 3). Genetic testing confirmed the diagnosis of DM1 with >50 CTG repeats in the DMPK gene.

Table 1.

Baseline Investigations.

Haemoglobin	8.8 g/dL
Peripheral smear	Microcytic hypochromic picture
Iron profile
Serum iron	35 µg/dL
Total iron binding capacity	450 µg/dL
Transferrin saturation	7%
Ferritin	8 ng/dl
Fasting blood sugar (FBS)	160 mg/dL
Postprandial blood sugar (PPBS)	200 mg/dL
HbA1c	6.2%
Lipid profile
Total cholesterol	294 mg/dL
Low-density lipoprotein (LDL)	188 mg/dL
Triglycerides	394 mg/dL
Total creatine kinase (CK)	Elevated (707 IU/L)

Figure 2.

Uroflowmetry Showing Poor Flow Pattern with a Prolonged Time to Maximum Flow (21.6 Seconds), a Maximum Flow Rate (Qmax) of 8.3 mL/sec, and an Average Flow Rate (Qavg) of 4.6 mL/sec—Findings Suggestive of Detrusor Underactivity.

Figure 3.

Myotonic Dive Bomber Discharges in Deltoid Muscle Right Side.

Management

Patient was initially put on clean intermittent catheterisation, which was changed into continuous silicon catheterisation due to improper technique and Bethanechol (muscarinic agonist) to improve bladder tone. Carbamazepine was given to improve myotonia. Diabetes mellitus was managed with oral hypoglycaemic agents, and patient was started on oral iron therapy for iron deficiency anaemia. Patient’s attenders were counselled for further follow-up of cardiac and ophthalmological evaluation.

Follow Up

Patient has been followed up for three months and has shown improvement in grip myotonia. Her quality of life has improved with continuous catheterisation; however, the risk of recurrent urinary tract infections has been explained, and the use of preventive antibiotics cover has been explained in the case that urinary tract infections occur.

Discussion

This case features a 31-year-old lady with genetically proven DM1 who developed an atonic bladder with recurrent urine retention, a rare and unrecognised symptom of the condition. DM1 is a multisystemic, autosomal dominant condition resulting from CTG repeat expansions in the DMPK gene, characterised by distal muscle weakness, myotonia, cataracts and cardiac conduction abnormalities. However, a growing amount of literature has highlighted its impact on smooth muscle and autonomic function, encompassing the gastrointestinal and genitourinary systems.^1–3

While the typical patient with DM1 presents with progressive muscle weakness and myotonia, our patient showed early-onset urinary symptoms—retention for over three years, ultimately found to be due to detrusor underactivity confirmed by uroflowmetry and significant post-void residual volume. This is in contrast to the more commonly reported urinary incontinence or urgency symptoms in DM1 cohorts. Fisette-Paulhus et al. (2022) reported urinary incontinence in 60% and pelvic floor disorders in over 50% of women with DM1, but detailed urodynamic evaluation confirming atonic bladder remains rarely documented. ⁴

The clinical features in this case—consisting of grip myotonia, frontal alopecia, ptosis, cognitive impairment and cataracts—aligns with classic DM1. Detrusor underactivity in DM1 is thought to result from a combination of smooth muscle dysfunction and autonomic nervous system involvement, as demonstrated by early urodynamic studies by Bernstein et al. (1992) and Vohanka et al. (2014).^{5, 6}

This patient met both clinical and electrophysiological criteria for DM1, demonstrating myotonic discharges on electromyography (EMG) and more than 50 CTG repeats on genetic testing. The bladder dysfunction in this patient had a significant impact on quality of life, underscoring that urogenital symptoms can be a prominent and disabling manifestation of the disease.

In management, Bethanechol was given to augment detrusor activity. Clean intermittent catheterisation is the recognised primary treatment for atonic bladder; nevertheless, due to procedural limitations, the patient transitioned to a continuous silicone catheter, which improved quality of life, but long-term infection risk remains. This trade-off is frequently encountered in neurogenic bladder treatment, requiring individualised care.

Conclusion

This case underscores the importance of recognising atypical manifestations of DM1, such as detrusor underactivity and chronic urinary retention. Atonic bladder, although rarely reported in the literature, can significantly impact the quality of life and renal health if not promptly identified and managed. Through detailed clinical, electrophysiological, and genetic evaluation, this case reinforces the need for a multidisciplinary approach and emphasises that lower urinary tract dysfunction can precede or coexist with classical neuromuscular features of DM1. Early urological assessment and individualised bladder management strategies should be considered essential components of comprehensive care in patients with myotonic dystrophy.