Nodular Dermatofibrosis in German Shepherds: Kidney-Linked Skin Nodules

Based on peer reviewed veterinary research · For educational purposes only · Updated September 2026 · 8 min read

What Is Nodular Dermatofibrosis in German Shepherds?

Nodular dermatofibrosis (NDF) is an inherited syndrome of German Shepherd Dogs characterized by multiple firm collagenous skin nodules, usually accompanied by bilateral renal cystadenocarcinomas (kidney tumors) and, in females, uterine leiomyomas (benign smooth muscle tumors). It was described in a study of 51 affected dogs by Moe and Lium (1997).

The skin nodules are made of dense, overgrown collagen. They are typically small, firm, and painless, and may be found on the limbs, head, and trunk. Dogs are usually middle-aged or older when nodules become noticeable.

The condition matters far beyond the skin. The nodules are frequently the first visible clue to serious internal disease, which is why recognizing them early gives owners and veterinarians time to monitor the kidneys. The syndrome has a human counterpart, Birt-Hogg-Dube syndrome, which is caused by mutations in the same gene.

What Causes Nodular Dermatofibrosis?

The cause is a germline mutation in the FLCN gene, which encodes folliculin, a tumor suppressor protein. Lingaas and colleagues (2003) identified a missense mutation in this gene in affected German Shepherds and linked it to the syndrome.

The disease is inherited in an autosomal dominant pattern. That means one mutated copy from either parent is enough, and each puppy of an affected parent has roughly a 50% chance of inheriting the mutation. Because the disease appears later in life, affected dogs are often bred before signs develop, which has allowed the mutation to persist in the breed.

When the tumor suppressor function is lost in a cell, the cell can proliferate abnormally. In the skin this shows up as collagen overgrowth, and in the kidney as multifocal cystic tumors. The process is slow, and dogs may live with nodules for years before kidney signs appear.

How Do Veterinarians Diagnose Nodular Dermatofibrosis?

Diagnosis combines the clinical picture, a skin biopsy of a nodule, and a genetic test for the FLCN mutation. Histology shows dense, well-organized collagen within the dermis, and a genetic test can confirm the mutation from a cheek swab or blood sample (Lingaas et al., 2003).

Because the kidney and uterus are involved, staging usually includes abdominal ultrasound, urinalysis, and blood work to assess kidney function. Ultrasound can reveal cysts and masses before clinical signs develop. Our guide to kidney disease and dog skin explains how kidney problems can also change the skin in other ways.

Not every nodule in a German Shepherd is NDF. Cysts, tumors, and infections can look similar, so any new lump should be sampled. You can use the Dog Skin Condition Checker to record what you are seeing before your visit.

Signs and Symptoms to Watch For

The earliest sign is usually multiple firm skin nodules, often noticed while grooming or petting. Kidney tumors may cause no signs for a long time. The table below summarizes what is reported across body systems.

Treatment and Management Options

There is no cure for the underlying genetic disease, so management focuses on monitoring and on treating complications. Skin nodules usually do not need treatment unless they ulcerate, rub on a collar or harness, or become infected. Surgical removal is possible for problem nodules. Kidney tumors are typically bilateral and multifocal, which makes surgery difficult, so many cases are managed with regular imaging and supportive care. Spaying is generally recommended in affected females because of the uterine tumors (Moe and Lium, 1997).

Owners should also be aware of related nodular conditions that can be confused with NDF, such as xanthomas in dogs and the systemic tumor effects covered in paraneoplastic skin syndromes.

Where nodules are irritated and the surrounding skin develops yeast overgrowth, Yeast Dermatitis Shampoo contains ketoconazole, an antifungal that inhibits ergosterol synthesis in the yeast cell membrane. It supports routine skin hygiene, but it does not treat the nodules, the kidney tumors, or the underlying mutation. Read more in our overview of yeast infections in dogs.

Prevention and Long-Term Management

Prevention relies on genetic testing before breeding. Because the mutation is autosomal dominant, removing affected dogs from breeding programs is the most effective way to reduce its frequency in the breed. Breeders and buyers can ask for DNA test results from parent dogs.

For affected dogs, discuss a monitoring schedule with your veterinarian, typically periodic abdominal ultrasound and urinalysis. Keep a dated photo log of the nodules and note any change in size, number, or surface.

Use a well-fitted harness that avoids pressure on nodules, and keep the skin clean and dry. Report changes in appetite, thirst, urine color, or energy promptly, because they may reflect kidney involvement.

Frequently Asked Questions

What is nodular dermatofibrosis in German Shepherds?

It is an inherited syndrome causing multiple firm skin nodules, usually together with kidney tumors and, in females, uterine tumors.

Is nodular dermatofibrosis linked to kidney cancer?

Yes. Most affected dogs develop bilateral renal cystadenocarcinomas, and the skin nodules often appear before kidney signs.

What gene causes nodular dermatofibrosis?

A mutation in the FLCN gene, which encodes folliculin, causes the syndrome and is inherited in an autosomal dominant pattern.

Can nodular dermatofibrosis be cured?

No. The genetic cause cannot be corrected, so care focuses on monitoring the kidneys and managing complications.

Sources

1. Moe L, Lium B. Hereditary multifocal renal cystadenocarcinomas and nodular dermatofibrosis in 51 German Shepherd dogs. Journal of Small Animal Practice. 1997;38(11):498-505.
2. Lingaas F, Comstock KE, Kirkness EF, et al. A mutation in the canine BHD gene is associated with hereditary multifocal renal cystadenocarcinoma and nodular dermatofibrosis in the German Shepherd dog. Human Molecular Genetics. 2003;12(23):3043-3053.
3. Miller WH, Griffin CE, Campbell KL. Muller and Kirk's Small Animal Dermatology. 7th ed. Elsevier; 2013.
4. Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Skin Diseases of the Dog and Cat: Clinical and Histopathologic Diagnosis. 2nd ed. Blackwell; 2005.

Related Reading

• Kidney Disease and Dog Skin: How Renal Failure Affects Skin Health
• Xanthomas in Dogs: Yellow Skin Nodules Linked to Fat Metabolism Disorders
• Paraneoplastic Skin Syndromes in Dogs: When Skin Changes Signal Internal Cancer

E. Maddens

Founder of Vetified. Develops topical antifungal and antimicrobial formulations for companion animals. Vetified products are listed on DailyMed and manufactured through FDA-registered facilities in the United States.

Research basis: All Vetified content references peer reviewed research published in journals including Veterinary Dermatology, JAVMA, and Journal of Small Animal Practice.