Myeloproliferative neoplasm (MPN)‐unclassifiable (MPN‐U) or not otherwise specified represents a rare, poorly defined and heterogeneous group of MPNs. Disease incidence is difficult to define but likely represents close to 5% of all MPNs when strict World Health Organisation (WHO) criteria are applied. Dynamic review over time is required to assess if the disease can be re‐classified into another MPN entity. A diagnosis of MPN‐U leads to many challenges for both the patient and physician alike including lack of agreed monitoring and therapeutic guidelines, validated prognostic markers and licenced therapies coupled with exclusion from clinical trials. MPN‐U has an inherent risk of an aggressive clinical course and transformation in some but who, and when to treat in the chronic phase, including identifying who may require more aggressive therapy at an earlier stage, remains elusive. Moreover, despite the significant thrombotic risk, there is no agreement on systematic primary thromboprophylaxis. We hereby provide a contemporary overview of MPN‐U in addition to four illustrative cases providing our collective suggested approaches to clinical challenges.

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Sir,We read with interest the paper by Sellers et al.[1], who elegantly reported 5-hydroxytryptamine (5-HT) potentiation of cholinergic responses to electrical ®eld stimulation in pig bladder strips. These authors speculated that altered 5-HT modulation of cholinergic responses might play a role in bladder dysfunction. The authors based their hypothesis on previous studies, which have postulated that altered cholinergic responses may be a possible cause of detrusor instability associated with BOO. We also considered the possible role of 5-HT in bladder dysfunction associated with BOO. To this effect we showed, in a rabbit model of partial BOO, that there is a signi®cant time-dependent upregulation of neuronal 5-HT binding sites in the detrusor [2]. We also showed that doxazosin, an a-antagonist used in treating BPH, signi®cantly inhibits 5-HT-mediated contractions in the rabbit detrusor [3]. Autoradiography showed that doxazosin reduced 5-HT binding to receptor sites in a concentration-dependent manner in this tissue [3]. Hence, we speculated that the bene®cial effects of doxazosin in BOO may be ascribable, at least in part, to 5-HT antagonism. These ®ndings support the hypothesis that 5-HT contributes to the pathogenesis of bladder dysfunction. A prospective study of conservatively managed acute urinary retention: prostate size mattersSir, The authors of this paper [1] conclude that`a trial without catheter is justi®ed in men presenting with AUR [acute urinary retention] arising from BPH', a statement which I believe to be true. It is also interesting to see a`real-life practice' study of a condition commonly met by urologists, particularly given the recent interest in AUR and its management, reviewed recently [2]. However, this study [1] has several major¯aws in its methodology which call into question any conclusions that may be drawn from the results. The authors report on the outcome of a group of 40 men presenting with`primary AUR' de®ned as`an episode of painful inability to void which was relieved by passing a catheter'. They claim to have excluded those men with lower urinary tract pathology which might have in¯uenced the natural course of BPE. Included in the study were three men who had had a previous episode of AUR; can they truly be described as having primary AUR? At least one individual said to have an acute retention had a residual volume of 2.8 L on catheterization, and there is no comment within the paper as to whether any patients had deranged renal function or not. Six patients included in the study had undergone a previous TURP, which of all the interventions offered by urologists must in¯uence the natural course of BPE most dramatically! There were also three men taking anticholinergic medication, and several already taking a-blockers. Of the 40 men who were included in the study, 16 were reported to have constipation on admission, which was relieved before a trial without catheter (TWOC). More men had a successful TWOC after clearance of their constipation than failed to void (10 vs six)...