Histiocytes are cells of the immune system that live in the tissues. Bernese Mountain Dogs are well known for problems with these cells: a genetics study of the breed notes that histiocytic sarcoma, a cancer of histiocyte-type cells, affects as many as one in four Bernese Mountain Dogs [3]. This article is about a different, non-cancer condition called systemic histiocytosis. Vets now often call it systemic reactive histiocytosis, because the cells grow in reaction to something rather than as a cancer [1][2]. Its skin lumps can flare up and then settle down again over time [1].
If your Bernese Mountain Dog has lumps on the skin, eyelids, nose or muzzle, see your vet.
What is going on in the skin
In this disease, activated immune cells called dendritic cells collect in the skin and the tissue just under it [1][2]. The exact cause is not known, and no germ has been found behind it [1][2]. Researchers think the immune system is out of balance, and genes may also play a part [1].
The disease comes in two forms. In the cutaneous form, it stays in the skin, the tissue under it and the nearby lymph nodes. In the systemic form, it also reaches other parts of the body, such as the lining of the nose or mouth, the eyes or the internal organs [1][2].
Skin signs
The skin lumps look the same in both forms [1]. In a recent case series of 10 dogs, one of them a Bernese Mountain Dog, every dog had several firm lumps in the skin or red, raised patches, often with some hair loss over them [1]. They were seen on the face (around the eyes and on the muzzle), the top of the head, the body and the legs, and in some dogs the patches broke open into sores [1].
Lumps that come and go
Reactive histiocytosis tends to flare and settle on its own, and lumps can sometimes clear up for a while without treatment [1]. That makes it hard to judge from the lumps alone how the disease is going, so regular checks with your vet matter.
Signs beyond the skin
In the systemic form, the nose is often involved. In one earlier study, more than half of 26 dogs with this form had changes inside the nose [1]. Signs to watch for include sneezing, noisy breathing through the nose, a runny nose and loss of colour on the nose. Lumps in the mouth or on the gums can also occur, so your vet may check the mouth carefully [1].
For the skin-only form of this disease, see cutaneous histiocytosis in dogs.
How it is diagnosed
A vet confirms the disease by taking a small sample (biopsy) of a lump and having it looked at under the microscope. Other causes, such as infections and some types of skin cancer, need to be ruled out first [1].
Treatment
The disease is thought to be driven by the immune system, and dogs have responded to medicines that calm the immune system [1][2]. Your vet will advise on treatment for your dog.
At home, as directed by a vet:
- do not open, squeeze or drain a lump yourself;
- do not give your dog human or leftover medicines unless your vet says so;
- do not stop or change any medicine without talking to your vet;
- go back for any recheck your vet books.
Outlook
Studies report that the systemic form is harder to control than the skin-only form, can follow a more serious course, and more often leads to the decision to put a dog to sleep [1].
These are statements about groups of dogs. They cannot predict how one dog will do. Your vet can explain what this means for your dog.
When to see your vet
See your vet if your dog has:
- firm lumps or red, raised patches in the skin, for example around the eyes or on the muzzle [1];
- lumps with hair loss over them, or lumps that break open into sores [1];
- skin lumps that go away and then come back [1];
- sneezing, noisy breathing through the nose, a runny nose or loss of colour on the nose [1];
- any lump you are unsure about.
The bottom line
Systemic histiocytosis is an immune-driven, non-cancer disease that causes lumps in the skin and can also affect the nose, mouth, eyes or internal organs. The lumps can come and go. Only a vet can find the cause of a lump.
This article is for general information only and does not replace advice from your veterinarian. If your Bernese Mountain Dog has lumps on the skin, see your vet.
Sources
- Cain CL, Lowe A, Mauldin EA. Treatment of Reactive Histiocytosis With Oclacitinib: A Retrospective Case Series of 10 Dogs. Veterinary Dermatology. 2026. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC13167641/
- Affolter VK, Moore PF. Canine cutaneous and systemic histiocytosis: reactive histiocytosis of dermal dendritic cells. American Journal of Dermatopathology. 2000;22(1):40-48. PubMed abstract. https://pubmed.ncbi.nlm.nih.gov/10698216/
- Meek K, Yang YT, Takada M, et al. Identification of a Hypomorphic FANCG Variant in Bernese Mountain Dogs. Genes (MDPI). 2022. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC9601343/