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Nail pathologies

Broken nails are common but it is another matter when all the feet are involved and nails start falling out

01 May 2020, at 7:45am

One patient of note was a male neutered Rhodesian Ridgeback aged seven years and nine months when he was presented in discomfort with three lost claws and some of the others hanging loose. He was anaesthetised and his nails were clipped back. A swab of the nailbed showed a profuse growth of Escherichia coli and a moderate growth of Malassezia. I first met this dog when he came in for a post-operative check. His paws were unremarkable and the nails were healing, but he was dull and slightly pyrexic (103.2ºF). I started him on marbofloxacin and carprofen with an antimicrobial for topical application to the remaining nail tissue and an antimicrobial shampoo to clean his hair. His temperature was back to normal next day. In-house haematology and biochemistry were normal.

Having just moved house, his owners wondered if there could be an environmental trigger. He had no previous illnesses, he had not travelled abroad so leishmaniasis wasn’t an indication, his hair coat was good and he had no lesions on muco-cutaneous junctions which would indicate a diagnosis of pemphigus foliaceus, but the fact that multiple nails were affected did suggest immunosuppression. It was decided to amputate a dew claw and send this for histology as the site of interest was the nailbed itself.

This gave the diagnosis of mild to moderate lymphoplasmacytic onychitis which was chronic and multifocal. This inflammation of the nail bed leads to onychomadesis, loss of the nail. In this case there were small lymphocytes with fewer neutrophils and plasma cells, and some melanin-laden macrophages which indicated damage to the stratum basale and basement membrane of the epidermis. The nailbed epithelium was ulcerated and there was perivascular inflammatory infiltrate in the adjacent superficial dermis. There was some new bone formation in the bone of the distal phalanx close to the nailbed. There was no evidence of infectious agents. The patient moved again and was lost to follow-up.

The second case involved a four-year-old neutered female lurcher. When she went acutely lame on her left hind paw, I assumed that there was a traumatic cause for the one swollen digit. She resented palpation very strongly, so she was sedated. This allowed detection of a sloughing nail but no palpable fracture. I went on thinking of trauma until she continued to lose nails over the next few weeks and became miserable and reluctant to exercise. Six weeks after the initial nail loss we were considering that the involvement of many nails suggested an autoimmune condition.

Autoimmune skin diseases tend to be chronic and relapsing and the lesions can be severe. It was suggested that the patient’s symptoms would fit a diagnosis of lupoid onychodystrophy but histology of the nail and nailbed would be required to establish a diagnosis. As her dew claws had been removed by a previous owner, getting the right specimen required removing nail and nailbed from a weight-bearing toe. It was decided to try medication for some months to see if this intervention could be avoided. She was put on to biotin at 25mg per day, essential fatty acid supplements and meloxicam for pain relief. However, she was increasingly sore, lame, reluctant to walk and depressed.

So, the patient underwent general anaesthesia and the nail and third phalanx of the second digit of the left hind was removed. During the operation, it was noted that all her claws were affected. Most of the ungual folds had a dark brown ceruminous-like discharge. Smears were made from this and hair plucks taken. Some of her remaining claws were coming loose and they smelt infected. Two loose claws were sent for culture for dermatophytosis. The paw was bandaged and a course of amoxycillin/clavulanate started.

Her pathology report indicated a mixed infection comprising light growths of Staphylococcus pseudintermedius, Lancefield Group G Streptococcus, E. coli and Corynebacterium species. All were sensitive to amoxycillin/clavulanate. The smears of the ungual discharge showed a few bacteria in the cytoplasm of neutrophils. There were no yeasts or acantholytic cells. The mixed infection was most likely to be an overgrowth secondary to lupoid onychodystrophy which is also known as interface onychitis or lupoid onychitis.

Microscopic examination of the digit showed moderately severe chronic onychitis with mild interface damage. Interface onychitis involves abnormal claws and loss of claws in multiple feet. German Shepherds are predisposed to it. There may be no known cause though it may be autoimmune. In some cases, feeding a hypoallergenic diet can help. Urinalysis and blood tests are seldom contributory to the diagnosis. Treatments include prednisolone, essential fatty acid supplementation, doxycycline, niacinamide and pentoxifylline.

The lurcher was put on prednisolone at 2mg/kg per day once her wound had healed. After the first week, this was reduced to 1mg/kg per day and this was continued for the next three weeks, then 1mg/kg twice weekly. She has a hypoallergenic diet, and essential fatty acid and biotin 2.5mg/day supplementation. Her nails are not the best but her claws reach down to ground level now and she shows no signs of discomfort. She has been on this regime for the last year and it is likely that she will stay on it in the future.

Nailbed pathology proved to be a “bed of nails” in its impact on the patient’s well-being in both these cases