A surgical biopsy specimen, obtained from a draining tract near the footpad of a 4-year-old male, intact, German Shepherd dog, was submitted to the laboratory for evaluation. The submitting clinician provided a thorough clinical history which indicated a two-year duration of a chronic draining wound from the left metatarsal region just proximal to the metatarsal pad. This lesion had been previously biopsied and diagnosed as chronic, hyperplastic, ulcerative, pyogranulomatous dermatitis. Special stains for fungi and A acid-fast bacteria were performed with negative results. The dog was treated with various courses of antibiotics at which time the lesion seemed to improve yet never completely resolved.

The current biopsy specimen submitted to the laboratory was obtained from a similar lesion now developing in the right metatarsal region, again just proximal to the metatarsal pad. Upon microscopic examination, there was similar, extensive and severe, pyogranulomatous inflammation of the dermis and subjacent panniculus with necrosis, clefting, and tract-like formation. The overlying epidermis was hyperplastic and ulcerative, again similar to the microscopic findings two years prior from the lesion of the opposing limb.

Special stains for fungal agents and acid-fast bacteria were pursued again with negative results and no foreign body material was identified. Culture did reveal a heavy growth of both hemolytic and non-hemolytic Escherichia coli, as well as Staphylococcus aureus. However, while these agents were likely contributing to the observed inflammation, they were interpreted as secondary rather than primary pathogens.

Considering the signalment, clinical history, bilateral involvement, and lack of any identifiable primary inciting cause for the lesions, there was a high suspicion for a possible breed-specific idiopathic condition. Skin Diseases of the Dog and Cat, 2nd ed. was referenced and the entity Metatarsal fistulation of the German Shepherd dog also known as sterile pedal panniculitis and deep metatarsal/metacarpal toritis
(inflammation of the footpad) was identified. It was a perfect match.

Metatarsal fistulation of the German Shepherd dog is considered an uncommon dermatopathy which is characterized clinically by well demarcated, often symmetric, deep fistulous tracts of the proximal aspect of single or multiple pawpads (Fig. 1 - Olivera AM, et. al 2006). The metatarsal pads are affected most commonly followed by the metacarpal pads and, very rarely, other paw pads. The etiology is, as of yet,
undetermined however the breed predilection for the German Shepherd suggests heritability. Dogs also may present with concomitant perianal fistulas and / or interdigital bacterial furunculosis, conditions to which German Shepherds also are predisposed. An increased frequency has been noted in males as compared to females and adult dogs from 2-to-8-years old predominate. While the syndrome is primarily seen in
German Shepherds, cases in German Shepherd cross breeds (Kunkle 1993) as well as a single case in a Weimaraner (Oliveira 2006) also have been reported.

Differentials for this condition are few due to the unique clinical presentation. Fistulous tracts subsequent to foreign body material should be considered although the anatomical location of the lesion at the proximal portion of the footpad is a bit atypical for a penetrating foreign body. While clinical differentials are few, the microscopic features of hyperkeratosis, acanthosis, ulceration, marked pyogranulomatous dermatitis, and panniculitis, with or without the presence of tract formation depending on the location of biopsy acquisition, are fairly non-specific. These changes could be associated with deep bacterial or fungal infections, a foreign body reaction, or a traumatic penetrating wound. Thus, in the absence of salient clinical information including, at the forefront, signalment and anatomical location, the appropriate diagnosis of metatarsal fistulation of the German Shepherd dog could go undetermined.


In summary:
1. If you are a clinician presented with draining fistulous tracts of single or multiple foot pads in a German shepherd dog think metatarsal fistulation of the German Shepherd dog

2. If you are a pathologist presented with tissue from a draining fistulous tract of single or multiple foot pads in a German Shepherd dog think metatarsal fistulation of the German Shepherd dog

3. As microscopic lesions often may be non-specific, the provision of thorough clinical information may be critical in deriving the correct diagnosis such as with metatarsal fistulation of the German Shepherd dog. And. . . . last but not yeast,

4. Now you have heard of metatarsal fistulation of the German shepherd dog

Thank you to Dr. J. Flick at Flatirons Veterinary Specialists for the biopsy submission in this interesting and uncommon case, and for her thorough clinical history which assisted us in determining the diagnosis of metatarsal fistulation of the German Shepherd dog.
References:
Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Metatarsal fistulation of the German Shepherd dog. In: Skin
Diseases in the Dog and Cat. 2nd ed. 2005 Blackwell Publishing, Oxford. pp 553-555
Kunkle GA, White SD, Calderwood-Mays M, Polenz-Zertuche HO. Focal metatarsal fistula in five dogs. J
Am Vet Med Assoc. 202(5): 756-57, 1993
Oliveira AM, Obwolo MJ, Van Den Broek AM, Thoday KL. Focal metatarsal sinus tracts in a Weimaraner
successfully managed with ciclosoporin. J Sm An Pract 48(3): pp161-164, 2006