Enuresis and Urinary Incontinence in SMA

Involuntary wetting is one of the most common problems of childhood. One in 10 seven year-old children, for example, experience bedwetting, and about 6% of seven-year-olds wet themselves during the day.1 There is evidence to suggest, however, that the rate of enuresis and urinary incontinence in children and adolescents with spinal muscular atrophy (SMA) may be much higher. Indeed, in a survey of 96 children with severe SMA between the ages of six and 18 years, 29% involuntarily wet themselves at night and/or during the day.2 Incontinence was worst in children with SMA types 1 and 2. Like children without SMA, the rate of incontinence was higher in younger children than in adolescents.

Defining involuntary voiding

The International Children’s Continence Society has published a standardized terminology for describing conditions that affect the lower urinary tract in children and adolescents.3,4 Urinary incontinence is the involuntary leakage of urine either continuously or intermittently. Urinary incontinence is further divided into daytime incontinence and enuresis, i.e., incontinence that occurs exclusively during periods of sleep. Nocturia is waking at night to urinate. 

Separate terminology, that is still used by some organizations, further describe “functional” or “non-organic” enuresis as involuntary voiding in children five years of age or older when other organic causes of incontinence have been ruled out.5,6 According to the World Health Organization, to qualify as “non-organic” enuresis, it must not be caused by an epileptic attack, a neurological issue, structure on the realities of urinary tract, or other non-psychiatric condition.6

The etiology of enuresis and incontinence in patients with spinal muscular atrophy

The definitions that apply to involuntary voiding are particularly important for the management of patients with SMA because it is unclear whether urinary symptoms are caused by the pathophysiology of SMA (i.e. organic) or are the result of behavioral problems (i.e. functional/non-organic). Von Gontard and colleagues note that the rate of daytime incontinence and enuresis is five times higher than would be expected in a group of similarly aged children without SMA.2 This could suggest that muscle weakness was to blame for this excess incontinence. After all, SMA affects voluntary, striated muscles but not smooth muscles. Thus, the external urethral sphincter and pelvic floor muscles could be weak in children with SMA while detrusor muscles of the urinary bladder remain unaffected. This assertion, it should be mentioned, has not been demonstrated empirically. 

Alternatively, the rates of incontinence by age mirrored those seen across ages in otherwise healthy children. Wetting decreased from 45% in children younger than 11 years old to 13% in older children and adolescents.2 Thus, many children with SMA may have “functional” forms of urinary incontinence instead of or in addition to incontinence related to the disease itself.

Managing enuresis and urinary continence in patients with spinal muscular atrophy

Given the much higher rate of enuresis and urinary incontinence in children with spinal muscular atrophy, clinicians should be aware that wetting often occurs in this patient population and inquire about it. Pediatricians should ask about daytime incontinence and enuresis in all patients with SMA. This issue may be particularly relevant in children with SMA who still wear diapers beyond age 3 to 4 (in the United States, 98% of children achieve daytime continence by the age of 36 months7). Physicians should also determine if and how much the child’s incontinence affects the parents (i.e. is it burdensome? Would they prefer treatment, if possible?) Importantly, families often do not mention wetting problems and do not proactively seek treatment.2 If involuntary wetting is troublesome to patients or caregivers, a full urodynamic examination and referral to a pediatric urologist should be offered.2 

It may be particularly difficult to distinguish between organic and non-organic causes of involuntary wetting in children with SMA. A structured psychiatric interview could be viewed as the gold standard, but this is likely too time-consuming to be practical in most cases. Researchers have noted that the Child Behaviour Checklist is highly unreliable in assessing incontinence in patients with SMA. For example, a structured psychiatric interview revealed the rate of incontinence was 29% in the research cohort, but the Child Behaviour Checklist revealed a rate of only 17% in the exact same study group.2 Instead, researchers used an incontinence-specific questionnaire to help clarify the etiology of incontinence.8 Unfortunately, few incontinence-specific questionnaires, if any, have been validated in this patient population. The Pediatric Urinary Incontinence questionnaire is one such instrument—it is a quality-of-life tool specific to children who have bladder dysfunction9,10,11, yet it is unclear how relevant it would be in children with SMA. 

If the cause of enuresis and daytime incontinence is not directly related to muscle weakness, then children should receive standard care for these conditions as in otherwise healthy child would. On the other hand, involuntary wetting that is directly related to SMA may have no specific management options (other than disease-modifying treatments).

Lastly, constipation and encopresis are also common in children with SMA. Indeed the accumulation of rectal fecal masses can compress the bladder neck, prompt bladder contractions, and lead to wetting.12 Importantly, when constipation and wetting co-occur, administering an enema can sometimes ameliorate both conditions.2,8 


1. Jarvelin MR, Vikevainen-Tervonen L, Moilanen I, et al. Enuresis in seven-year-old children. Acta Paediatr Scand. Jan 1988;77(1):148-153.

2. von Gontard A, Laufersweiler-Plass C, Backes M, et al. Enuresis and urinary incontinence in children and adolescents with spinal muscular atrophy. BJU Int. Sep 2001;88(4):409-413.

3. Neveus T, von Gontard A, Hoebeke P, et al. The standardization of terminology of lower urinary tract function in children and adolescents: report from the Standardisation Committee of the International Children’s Continence Society. J Urol. Jul 2006;176(1):314-324.

4. Austin PF, Bauer SB, Bower W, et al. The standardization of terminology of lower urinary tract function in children and adolescents: Update report from the standardization committee of the International Children’s Continence Society. Neurourol Urodyn. Apr 2016;35(4):471-481.

5. von Gontard A. The impact of DSM-5 and guidelines for assessment and treatment of elimination disorders. Eur Child Adolesc Psychiatry. Feb 2013;22 Suppl 1:S61-67.

6. Organization WH. The ICD-10 classification of mental and behavioural disorders: diagnostic criteria for research. Vol 2: World Health Organization; 1993.

7. Augustyn M, Zuckerman BS, Caronna EB. The Zuckerman Parker handbook of developmental and behavioral pediatrics for primary care. Lippincott Williams & Wilkins; 2010.

8. O’Regan S, Yazbeck S, Hamberger B, et al. Constipation a commonly unrecognized cause of enuresis. Am J Dis Child. Mar 1986;140(3):260-261.

9. Bower WF, Wong EMC, Yeung CK. Development of a validated quality of life tool specific to children with bladder dysfunction. Neurourol Urodyn. 2006;25(3):221-227.

10. Schaeffer AJ, Diamond DA. Pediatric urinary incontinence: Classification, evaluation, and management. African Journal of Urology. 2014/03/01/ 2014;20(1):1-13.

11. Bower WF, Sit FKY, Bluyssen N, et al. PinQ: A valid, reliable and reproducible quality-of-life measure in children with bladder dysfunction. Vol 22006.

12. Yazbeck S, Schick E, O’Regan S. Relevance of constipation to enuresis, urinary tract infection and reflux. A review. Eur Urol. 1987;13(5):318-321.