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What are the lesions on this man's penis?

This man presented with a penile problem, but it took a full examination for Dr Oliver Starr to figure out the diagnosis

The patient

This 59-year-old man was generally very healthy and in fact hadn't consulted us for two years. But some skin lesions had developed on his penis in just a matter of days. Understandably concerned, he had seen the out-of-hours GP over the weekend who had thought it was a fungal infection and prescribed some miconazole cream and – presumably in case it was folliculitis – some flucloxacillin for good measure. Two days later it was no better.

Examining him, he looked well but there were these scattered dark red spots on the shaft of his penis. I wasn't sure what they were and, putting on some gloves, asked if I could touch. The patient gave a sharp intake of breath as I ran my finger over the lesions. They were exquisitely painful.

Differential diagnoses

• Fungal skin infection

• Bullous impetigo

• Herpes simplex

• Shingles (herpes zoster)

On first look I would have agreed with my out-of-hours colleague. Fungal skin infections are quite common around the groin, although they are usually larger and plaque like. The most common pathogens are Candida albicans and the dermatophyte fungus Tricophyton rubrum. With the benefit of two days' follow-up, I could see the miconazole wasn't helping.

Impetigo is caused by Streptococcus pyogenes and Staphylococcus aureus. We are used to seeing it in classic crusted yellow form around the mouths of children, hence its nickname ‘school sores'. Bullous impetigo, although caused by the same organism, gives a blistered appearance. Some 15-40% of healthy humans are colonised by Staphylococcus aureus, usually in the nostrils and flexures. 

Surely this patient was the wrong age for genital herpes? I asked tentatively about his sexual relations and he'd been married to the same woman for longer than he could remember. As for extra-marital relations: ‘No such luck, doc.' This left singles as a distinct possibility. From an initial varicella zoster infection (chickenpox), the virus lies dormant in the nerve cell bodies. Years later, for unknown reasons, it travels down the axon to cause a painful infection of the skin in a dermatome: shingles. Systemic malaise accompanies this. Interestingly there is a condition with all the symptoms of shingles, but without the rash: zoster sine herpeticum.

Getting on the right track

The clue was the painful nature of these lesions. I knew I was onto a viral infection.  The important thing was to examine the whole patient. He mentioned a similar sore sensation on his left buttock and, examining him, I found a faint vesicular rash which was also very tender to touch.

Glancing at a dermatome map on my wall, I saw how it all fitted together. This was shingles, in the S2 dermatome.

A week later, the sores had crusted over and he felt under the weather. Six weeks later, he was well and the rash had cleared.

Dr Oliver Starr is a GP in Stevenage, Hertfordshire

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