Spot on penis

by Barbara
(Bend, OR USA)

Reader Question My 10.5 year-old lab/pointer cross has a single spot on penis also has what could either be related or non-related site on upper lip. Original spot on penis was slightly raised, opaque and red with smooth margins. Within 2 weeks spot changed to pink, translucent and margins are irregular.

Area on face has become larger and pustules are numerous.

Dog taken to Vet a week ago, Vet unsure advised me to take a wait and see approach.

Suggestion from our publisher

Hi Barbara,

Thank you for the detailed description and for the dated photos, which make the changes easy to follow. I'm not a veterinarian, so I can't tell you what these are, but I can share what the pattern suggests and why I would not be comfortable with open-ended "wait and see" here.

What stands out

Two lesions in two different places (the lip and the penis) in a 10.5-year-old dog.

Both sit at or near a mucocutaneous junction, the places where haired skin meets moist mucous membrane (lips, nose, eyelids, prepuce, genitals, anus). Certain conditions have a particular liking for these areas, which is why a lip and a penile lesion appearing together is worth taking seriously.

Both have changed over a short time. The penile spot went from smooth and opaque to translucent with irregular margins, and the lip lesion has grown with more pustules. Lesions that are changing, growing, or developing irregular edges are the kind vets generally want to sample rather than just monitor.

Possible causes

Mucocutaneous pyoderma. A bacterial infection of the junction areas, most often the lip margins, but it can also involve the prepuce and genitals. It looks red, crusty, or pustular and often responds to a course of antibiotics, which makes it one of the more hopeful possibilities.

Pemphigus (an autoimmune skin disease). The immune system attacks the skin, producing pustules, erosions, and crusts, typically around the lips, nose, eyes, and genitals. It is diagnosed by biopsy and managed with immune-suppressing medication.

Cutaneous epitheliotropic lymphoma. A skin cancer of lymphocytes that mainly affects older dogs and often shows up on the lips, nose, eyelids, and other mucocutaneous junctions. It can mimic infections and autoimmune disease, and it can only be confirmed with a tissue biopsy, since cytology (cells collected with a needle) is not enough to identify it.

Tumors of the penis, prepuce, or lip. Squamous cell carcinoma, mast cell tumors, and papillomas (warts) can all occur in these areas. Most are not related to each other, so a lip tumor and an unrelated penile tumor are possible, though two separate ones at once would be less likely than one condition causing both.
Balanoposthitis and lymphoid hyperplasia. Inflammation of the penis and prepuce from bacterial overgrowth, a foreign body such as a grass awn, or trauma. Small pink lymphoid nodules on the penis are also common and usually harmless in older intact dogs, but they do not explain the lip.

Lupus-type or other immune-mediated disease, or an allergic reaction. These can also affect the lips and genitals and are on the list vets consider.

What I would do

Ask for a biopsy or at least cytology of both lesions. This is the step that separates infection from autoimmune disease from cancer. Because epitheliotropic lymphoma cannot be diagnosed from cytology alone, a punch biopsy of the lip lesion (sometimes both) sent to a veterinary pathologist is the most informative test.

Ask for a culture if pustules are present, so any bacteria can be identified and treated with the right antibiotic.
Consider a second opinion or a referral to a veterinary dermatologist. Your vet being unsure is honest, and a specialist can often biopsy and diagnose quickly.

Keep a photo log with dates, like the ones you have already started, measuring against a coin or ruler. It gives your vet objective evidence of the pace of change.

Set a short deadline for "wait and see." If the lip lesion keeps enlarging, either lesion bleeds, ulcerates, or becomes painful, or your dog stops eating or seems unwell, go back sooner. I would not wait more than another week or so before pushing for a sample.
Avoid home ointments or squeezing the pustules, since that can muddy the picture and may delay a diagnosis.

Many of these possibilities, especially mucocutaneous pyoderma, respond well to treatment, and even the more serious ones are best handled when found early, which is why getting an actual answer matters more than guessing. I hope you get clarity soon, Barbara. Please let us know what the vet finds.

— The Dog Health Guide Team

This response is intended to provide general information and perspective for pet owners and is not a substitute for veterinary diagnosis or care.

Sources:

• Cutaneous epitheliotropic T-cell lymphoma in canines (Vet Times)


• Pemphigus Vulgaris (Univ. of Minnesota Animal Dermatology)


• Mucocutaneous Pyoderma in Dogs


• Balanoposthitis in Dogs and Cats (Merck Veterinary Manual)


• Disease of the canine penis and prepuce