Interdigital ‘cysts’ are a common, recurrent and painful problem in many dogs.  Treating the secondary infections will often result in only a short to medium term resolution. Recurrence is very likely unless the primary cause is detected & treated. The paw(s) may be inflamed only, or inflamed and infected with any combination of microbes (bacteria &/or yeasts), and/or with parasites.

The factors, causing Pododermatitis, digital and interdigital inflammation and infection, can be divided into four categories – primary, predisposing, perpetuating & secondary – listed below. Many of these factors, often in combination, can lead to the development of interdigital ‘cysts’.

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Primary causes
These factors directly induce paw inflammation (pododermatitis):

TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Autoimmune Diseases – Pemphigus foliaceus (uncommon), Pemphigus vulgaris (very rare), Epidermolysis bullosa (very rare), Systemic lupus erythematosus (very rare)
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Cornification Disorders – Paw pad hyperkeratosis, Familial Hyperkeratosis
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Endocrine – Hypothyroidism, Hyperadrenocorticism
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Foreign bodies Grass seeds/awns (very common), Thorns (hawthorn etc), Loose hair, stone, sand, salt etc
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Hypersensitivity Atopic dermatitis (common), Adverse food reactions (food allergy or dietary intolerance), Contact hypersensitivity (uncommon)
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Immune-mediated Adverse Drug Reactions (uncommon), Dermatomyositis (rare), Idiopathic Sterile Granuloma/Pyogranuloma (uncommon), Lymphoplasmacytic pododermatitis (primary or chronic end-stage?) –  Antibacterial-responsive (AbR-LPP) & Immunomodulatory-responsive (ImR-LPP), Plasma Cell Pododermatitis (cats), Symmetric Lupoid Onychodystrophy (or onychitis), Vasculitides (uncommon)
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Inflammatory – Reactive Histiocytosis
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Metabolic – Calcinosis circumscripta, Hepatocutaneous Syndrome (Superficial Necrolytic Dermatitis), Vitamin A Responsive dermatosis, Xanthomas, Zinc Responsive Dermatosis
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Microorganisms – Bacteria esp. Mycobacteria (rare as primary cause), Dermatophytosis – Microsporum canis etc (uncommon), Malassezia Yeast (rare as primary cause)
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Multifactorial – Acral lick dermatitis
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Neoplasia – Fibrosarcoma, systemic/malignant Histiocytosis, Epitheliotropic Lymphoma, Mast Cell tumour, Melanoma, Soft Tissue sarcoma, Squamous Cell carcinoma,  atrichial Sweat gland tumour, etc. & any metastases
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Orthopaedic – Congenital limb deformity, Cruciate disease, Degenerate joint disease/osteoarthritis, Elbow/Shoulder osteochondrosis dissecans
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Postural – Abnormal Gait/Conformation
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Parasites – Demodex canis mites (common), Hookworms (uncommon), Leishmaniosis (uncommon), Pelodera strongyloides (rare)
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Predisposing factors
These factors increase the risk of development of paw inflammation (pododermatitis) but do not directly induce it:

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TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Obstructive disease – benign cutaneous neoplasia
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Orthopaedic – Congenital limb deformity, Cruciate disease, Degenerate joint disease/osteoarthritis, Elbow/Shoulder osteochondrosis dissecans
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Physical – Excess bodyweight, Large & Giant breed dogs
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Postural – Abnormal Gait/Conformation
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Systemic disease – Immune suppression, Generalised neoplastic disease, Debilitation and negative catabolic states

Some of these factors can be considered Primary too.

Increased weight bearing on haired palmar and plantar pad margins → tissue hypertrophy and hyperplasia → focal hairshaft trauma → furunculosis → subcutaneous keratin-driven inflammation (endogenous foreign body reaction)

Perpetuating causes
These factors prevent complete resolution of the disease, sometimes permanently.

TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings.  Chronic, severe lymphocytic-plasmacytic inflammation
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Persistent endogenous foreign body reaction (keratin)
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Progressive pathological changes (from chronic inflammation and recurrent infections) – Destructive osteomyelitis, Dermal fibrosis – scarring, Epidermal hyperkeratosis, Follicilitis and furunculosis, Glandular hyperplasia/dilatation, Hidradenitis, Hyperplasia and Hypertrophy – increased epithelial folds/abnormal new pad growth/conjoined pads; Oedema – swelling

Secondary infections
Microbial infections, which are almost never primary, often cause the more acute clinical signs and this further progression leads to another visit to the Vet.

TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings.  Yeast Malassezia pachydermatis, Candida sp.
TheSkinVet.net logo is a stylised Maori Koru which represents an unfurling fern frond as it opens bringing new life to the world. Traditionally it signifies a strong sense of nurturing, regrowing or new beginnings. Bacteria Staphylococcus pseudintermedius, (Streptococcus sp.), Pseudomonas sp. (Proteus sp., Escherichia coli etc.)

Therefore the more interdigital granulomas that a patient undergoes the more difficult it may be to reverse the progression of paw inflammation (pododermatitis).

Eventually permanent damage will ensue and surgical treatment will be the only option through re-referral to a Soft Tissue Surgeon for major salvage surgery (surgical laser ablation or fusion podoplasty).

Download your Interdigital Cyst Advice sheet here: TheSkinVet Recurrent Interdigital ‘Cysts’ Information Sheet (PPPS)