Mitochondrial disorders are a group of phenotypically, biochemically and molecularly heterogeneous genetic diseases resulting from diminished cellular energy production due to impaired oxidative phosphorylation. There is multisystem involvement with tissues with high energy demands being particularly vulnerable. Some studies have shown that the gastrointestinal (GI) system can be affected, with slowed GI motility resulting in constipation and pseudo-obstruction. However, there had been no studies evaluating changes in lower urinary tract (LUT) functions in mitochondrial disease. Recently, we have shown that patients with mitochondrial disorders experience more urinary symptoms compared with healthy controls. But the pathophysiological basis for LUT dysfunction is poorly characterized in this group. The purpose of this study was to evaluate the urodynamic findings in a cohort of patients with mitochondrial disorder reporting lower urinary tract symptoms.

Fourteen patients with mitochondrial disorders were enrolled and investigated by uroflowmetry and/or measurement of postvoid residual urine volume (PVR). Four patients were also investigated by urodynamic study (UDS).

The mean maximum flow rate (Qmax) was 20.16 ml/sec (SD: 9.768) and three of 12 patients who underwent uroflowmetry had a low Qmax (<10ml/sec). Nine patients have abnormal findings of uroflow rate curve - intermittency, irregular stream and prolonged flow. The mean PVR was 87.93 ml (SD: 129.1). Seven of 14 patients who underwent measurement of PVR had over 30 ml PVR and 5 of them had about or over 100 ml PVR. One of 4 patients who were investigated by UDS had detrusor overactivity (DO) and another one had increased bladder sensation (bladder volume at first sensation was 62ml; bladder volume at strong desire to volume was 234ml) without DO during storege phase. Low Qmax was found in 3, low Pdet at Qmax was found in all 4 UDS recordings and AG number was low (<20) in all during voiding phase, suggesting detrusor underactivity without bladder outlet obstruction.

In this preliminary study, storage dysfunction such as DO and increased bladder sensation without DO was found in some patients with mitochondrial disorders. Low flow rate and large PVR due to detrusor underactivity appears to be a coomon in patients with mitochondrial disorders. The cause for this is uncertain, however may reflect involvement of bladder and the nervous system controled LUT and diminished cellular energy production which is characteristic of this condition. Caution is therefore advised when commencing patients on treatments for overactive bladder symptoms such as antimuscarinic agents in view of the increased risk for developing incomplete bladder emptying.  Despite the high prevalence of storage symptoms in this group, objective changes in UDS are variable and can include DO and early perception of bladder filling.

Significant pathophysiological changes in LUT control are seen in patients with mitochondrial disorders. Detrusor underactivity appears to be a common finding , despite the paucity of voiding symptoms. This implication may be useful in estimating the pathological condition and planning of the management for LUT sympotms in these patietns.