Patients with overactive bladder do not respond equally to medical treatments. This suggests that there may be different subgroups of women who have overactive bladder symptoms but have a different pathology.  The aim of this study is to determine in a large group of women with lower urinary tract symptoms whether there are different groups having nocturia or bladder pain as these women seem to respond differently to therapy.

Women were recruited from a university urogynaecology clinic.  They all completed a validated structured urinary symptom questionnaire and a five day bladder diary.  The symptom questionnaire used a six point Likert scale and all women indicating that they had urinary urgency were classified as having overactive bladder (OAB) in line with the ICS terminology for "overactive bladder syndrome (OAB) is characterized by urinary urgency, with or without urgency urinary incontinence, usually with increased daytime frequency and nocturia, if there is no proven infection or other obvious pathology".  Urinary tract infections were excluded by a negative urinalysis.
The urinary symptoms collected involved urgency, urgency urinary incontinence, stress urinary incontinence, incomplete bladder emptying, poor stream and bladder pain.  Nocturnal voids were recorded from the bladder diary.  Women were classified as having nocturia if the were under 60 years of age and voided more the once at night.  If the women were between 60 to 70 years of age then the cut off for nocturia was 2 voids in the night.  If the women were over the age of 70 then a cutoff over 3 voids at night was considered abnormal.

Three thousand and four hundred and twenty eight women were recruited. Overall 1781 women were classified as having an overactive bladder.  A likert scale questionnaire was asked about bladder pain.  Overall 2452 women felt they had a degree of bladder pain. However when comparing the bladder pain with the overactive bladder symptoms we find that only 3% of women with an overactive bladder had no bladder pain.  Although only 81% of women with overactive bladder felt the lowest level of pain. Overall of the women without overactive bladder, 58% had no bladder pain.

		pain score						                                        Total
		                0	        1	          2	         3	       4	      5	
No OAB	             919	      674	        32	         2	      18	      2	1647
OAB symptoms  57	     1445	       123	        33	     106	     17	1781
Total		     976	      2119	       155	        35	     124	     19	3428
Table 1: Overactive bladder symptoms against pain score (Pearson Chi Sq 1193.6, P<0.0001)

When assessing nocturia, we found that of those who did not have overactive bladder symptoms 1452 women (42%) had nocturia, but 64% of the women with OAB, also had nocturia (1145/1781).  Just assessing the OAB women we found that there were only 59 women (5%) who had OAB, nocturia and scored zero for pain.

The symptom of bladder pain plays a key role in overactive bladder symptomatology.  This may suggest a role in the development of OAB symptoms or possibly that OAB and bladder pain are on a spectrum of disease.  This would seem reasonable as both are C nerve fibre based syndromes and they both result in frequency and urgency.
Bladder pain plays a fundamental role in women having nocturia and overactive bladder such that 95% of women with OAB and nocturia also had bladder pain.  This could suggest a new subcategory of nocturia due to bladder pain.

Overactive bladder symptoms appear to be related to bladder pain and this could suggest a joint aetiology or a spectrum ranging from pure OAB to pure bladder pain.  This may indicate the reasons for the some patients with OAB who do not respond to treatment.