A pivotal pedicure: Understanding SLO

Courtesy of Jill Abraham, VMD, DACVD

Symmetrical lupoid onychodystrophy (SLO) is the most common inflammatory disease to cause abnormal nails in dogs. The etiology of this condition is unknown, but it is suspected to be hereditary or immune-mediated. SLO normally involves multiple nails on all four paws. It's most commonly seen in middle-aged dogs, around 3 to 8 years of age, but has been seen in both puppies and older dogs. Predisposed breeds include German shepherds, Rottweilers and Gordon setters, but it has been seen in other breeds as well.

The disease often starts as an acute onset of nail loss. Because SLO often starts with a single abnormal nail, it can often take owners a while to realize there is a more generalized nail problem. It may take several months for other nails to be affected or slough off. Nails can also present as dry, distorted claws that do not slough on their own.

One or more of the following abnormalities are typically seen over time:

• Onychogryphosis: abnormal curvature of the claws

• Onychomadesis: sloughing of claws

• Onychorrhexis: fragmentation of the claws

• Onychoschizia: splitting of the claws

In some cases (although less commonly), significant inflammation (paronychia) or purulent discharge from the nail bed may be present if there is a secondary bacterial infection. Dogs with this disease may by asymptomatic, but many can have associated discomfort or lameness. SLO is not typically seen with other skin abnormalities or systemic illnesses.

Differential diagnosis

Be sure to keep these alternative causes in mind when making your official diagnosis:

Bacterial claw infection

Dermatophytosis or deep fungal infection

Immune-mediated diseases:

Pemphigus vulgaris

Bullous pemphigoid

Lupus erythematosus

Vasculitis

Drug eruption

Neoplasia (squamous cell carcinoma)

Cryoglobulinemia or cold agglutinin disease

Keep in mind that fungal and bacterial infections will often affect more than one paw. Immune-mediated diseases can also affect multiple nail beds or paws. Neoplastic conditions more commonly affect a single digit or paw.

Diagnosis

We often diagnose SLO based on history and clinical signs. Certain tests will help us determine if there is a secondary infection that needs to be treated. Skin cytology or culture can be helpful if we see significant paronychia. A fungal culture can rule out dermatophytosis. A trichogram or skin scrape can rule out demodicosis.

Confirmation of the diagnosis necessitates surgical amputation of an affected P3 for dermatohistopathology. Unfortunately, the nail alone will not give adequate information; the junction between the affected nail bed and P3 is required. However, many veterinarians simply begin empirical treatment rather than performing an amputation. In cases that are biopsied, histopathology often shows hydropic degeneration of the basal cell layer, a lichenoid interface dermatitis and pigmentary incontinence.

General treatment information

It is important to give pet owners realistic expectations when it comes to clinical response to treatments. It will often take 12 weeks to see significant improvement-claws grow very slowly. The first sign of improvement is normal-appearing growth at the base of the claw.

Many treatment options exist; in my practice, we often use a combination of therapies or have to adjust treatment plans if there is minimal improvement or disease progression over several months. There is also no general consensus as to whether and when treatment should be discontinued. SLO is often treated for at least 6 months after remission of clinical signs, but certain cases will require life-long treatment. Medications should be tapered slowly and rechecks performed on a regular basis to monitor for signs of relapse.

Specific treatments

Nail care:

• Frequent trimming of nails (about every 2 weeks) to prevent further cracks

• Manual removal of loose nails (general anesthesia is often recommended)

• Treatment with appropriate antibiotics if secondary bacterial paronychia is present

• Omega-3 fatty acids
• 180 mg EPA/5 kg every 24 hours

• Often used in combination with vitamin E

• Vitamin E: 200 to 400 IU by mouth every 12 hours

• Tetracycline (doxycycline) and niacinamide
• Dogs weighing less than 10 kg: 250 mg of each by mouth every 8 hours

• Dogs weighing more than 10 kg: 500 mg of each by mouth every 8 hours

• Doxycycline (can be used in place of tetracycline): 5 to 10 mg/kg by mouth every 12 hours 

• Remember that niacin and niacinamide are two different products-make sure owners purchase the correct one (usually over the counter).

• Pentoxifylline: 10 to 25 mg/kg by mouth every 8 to 12 hours

• Cyclosporine: 5 to 10 mg/kg by mouth every 24 hours, then tapered to the lowest dose possible that prevents relapse

Prednisone:

• Often reserved for cases that have failed other treatments

• 2 to 4 mg/kg/day for about 2 to 4 weeks, then tapered slowly to reach the lowest every-other-day dose that prevents relapse

Azathioprine:

• 1.1 to 2.2 mg/kg by mouth every 24 to 48 hours

• Monitor CBC and liver enzymes every 2 weeks for at least 2 months.

• Consider pain control, particularly in the early stages of the disease.

• Consider a food elimination trial if there is a suspicion of an adverse food reaction based on history and diagnostics.

• Make sure dogs with hypothyroidism are supplemented appropriately as some dogs with SLO have had concurrent hypothyroidism.

• Onychectomy may be considered for refractory cases associated with onychalgia (pain).

Prognosis

The overall prognosis is good but owners should be aware that claws may continue to break easily and remain deformed. Outcome will depend on control of secondary infections, response to therapy and client compliance. Overall, the majority of dogs show some improvement within three to four months of starting treatment.

Dr. Judy Seltzer graduated from the Royal Veterinary College in London and completed her residency in dermatology at the University of Florida. She has been working in her home state of New York since 2009, currently at BluePearl Veterinary Partners in New York City. She and her husband have a baby girl and four cats and enjoy traveling, fall festivals, winter activities and dining out.