Letter to the Editor Intracavernosal PGE1-related penile ®brosis: possible mechanisms. The editorial comment made by Professor Porst on penile ®brosis following intracavernosal (i.c.) pros- taglandin E1 (PGE1) injection therapy for erectile dysfunction is very timely. 1 We reported 2 a 10% incidence of distal penile ®brosis following long-term use of i.c. PGE1. In this study, this complication was not related to the injection site as the lesions occurred distally. Since these patients achieved a grade IV erection lasting between 1±2 h, the development of ®brosis could not have been associated with inadequate erections. To explain why our patients developed distal penile ®brosis, we suggest two mechanisms. Firstly, it is well known that with aging there is signi®cant reduction of elastic ®bers in both layers of the tunica albuginea. 3 As a result, there is a signi®cant decrease in the elasticity of both the inner and septal ®brous layers supporting the tunica albuginea. Reduction in elastic ®bres and its elasticity prevents the corpora from tolerating relatively high i.c. pressures during PGE1-induced erections. This may result in tunical tears, disrup- tion of small blood vessels, bleeding and clot formation. This could subsequently result in ®bro- sis. Secondly, an ischaemic injury to the tunica albuginea may be involved in distal penile ®brosis. Assessment of blood ¯ow by duplex sonography has shown a signi®cant reduction in the blood ¯ow velocity in a proximo-distal direction following i.c. vasoactive injections. 4 Furthermore, the cavernous oxygen tension is signi®cantly lower after i.c. injection of PGE1 in arteriogenic and venogenic groups, compared to controls. 5 In animal experi- ments, there is shunting of blood from the sub- tunical space into the deep cavernosal circulation during both pelvic nerve and pharmacological stimulation. This shunting is more marked after pharmacological stimulation causing a greater drop in the subtunical oxygen tension in this group. 6 These changes may be responsible for inducing relative ischaemia and may have contributed to the formation of distal ®brosis in our patients. A more careful titration of the dose of PGE1 may reduce the incidence of distal penile ®brosis. The minimally effective dose, which achieves an ade- quate erection for the minimum length of time needed for patient satisfaction, should be used. FH Mumtaz 1 , MA Khan 1 , DP Mikhailidis 2 and RJ Morgan 1 1 Department of Urology and 2 Department of Chemical Pathology and Human Metabolism, Royal Free Hospital and School of Medicine, London NW3 2QG References 1 Prost H. Editorial comment: Penile ®brosis in intracavernosal prostaglandin E1 injection therapy for erectile dysfunction, by KK Chew et al. Int J Impot Res 1997; 9(4): 229±230. 2 Mumtaz FH et al. Prostaglandin E1 intracavernosal injec- tionsÐLongerm results and complications. Int J Impot Res 1996; 7: 120. 3 Akkus E et al. Structural alterations in the tunica albuginea of the penis impact of Peyronie's disease, ageing and impotence. Br J Urol 1997; 79(1): 47±53. 4 Iacono F, Barra S. Assessment of blood ¯ow in differ- ent segments of the penis by duplex sonography in sub- jects with normal erectile potency. Eur J Radiol 1994; 19(1): 60±64. 5 Sattar AA et al. Cavernous oxygen tension and smooth muscle ®bers: relation and function. J Urol 1995; 154: 1736±1739. 6 Azadzoi KM et al. Hemodynamics of penile erection: III. Measurement of deep intracavernosal and subtini- cal blood ¯ow and oxygen tension. J Urol 1995; 153: 521±526. International Journal of Impotence Research (1998) 10, 195 ß 1998 Stockton Press All rights reserved 0955-9930/98 $12.00 http://www.stockton-press.co.uk/ijir