Case Report Cutaneous Habronemiasis in a 9-Year-Old Arab Gelding in the United Kingdom S
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4 EQUINE VETERINARY EDUCATION / AE / JANUARY 2009 Case Report Cutaneous habronemiasis in a 9-year-old Arab gelding in the United Kingdom S. S. Down*, I. Hughes and F. M. D. Henson Queen’s Veterinary School Hospital, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK. Keywords: horse; nematode; habronema; cutaneous habronemiasis; granuloma Summary appearance and treatment of cutaneous habronemiasis in the pastern region of an adult horse and is presented as Cutaneous habronemiasis causes ulcerative granulating an example of a differential diagnosis that should be lesions in the skin of equids. Dramatic exuberant tissue considered when investigating possible neoplastic lesions may be seen, which becomes traumatised by the horse. of the limbs in horses. To the authors’ knowledge, cutaneous habronemiasis has not previously been documented on the distal limb of Case details horses in the UK. Cutaneous habronemiasis should be considered as a potential differential diagnosis for History ulcerative granulating skin lesions on the distal limb of the horse. A 9-year-old Arabian gelding was presented to the Queen’s Veterinary Hospital, for investigation and Introduction treatment of a ulcerated mass on the dorsum of the right fore pastern, 1 cm proximal to the coronary band (Fig 1). Cutaneous habronemiasis is a well recognised cause of The mass had first been presented to the referring skin lesions of the horse in tropical and temperate veterinary surgeon 10 months previously. At this stage the climates. The disease is caused by infection with the owner reported a small, nonulcerated, nonpainful nodule. larvae of the nematodes, Habronema muscae, The mass was then seen to increase in size and ulcerate, Habronema microstoma or Draschia megastoma. particularly in the 3 months prior to referral. Intermittent The pathogenesis of the condition has been well haemorrhage had been seen. The gelding was seen to described and it has been shown that infectious bite the heel bulbs of the affected limb on regular nematode larvae are deposited in moist areas of the skin occasions. No treatment had been undertaken. There was and pre-existing wounds. no history of previous disease or illness. The habronema larvae cause non-neoplastic The gelding was turned out to pasture 24 h a day. Fly ulcerative nodules in the skin, which may be multiple or repelling agents had been placed over the nodule, as this solitary, and can induce an excessive granulation tissue was an area of fly aggregation. The gelding had been response at the site of infestation. It is thought that this is treated with anthelmintics on a regular basis, but the field due to a hypersensitivity reaction. Areas of predisposition have been described to include the prepuce, urethral process of the penis and medial canthus of the eye. Infection of the distal extremity has also been noted in the tropics. To our knowledge there has not been a case of cutaneous habronemiasis reported in the UK within the last 20 years, with the only other report being in 1984 (Trees et al. 1984). This Case Report describes the presentation, *Author to whom correspondence should be addressed. Present address: The Centre for Equine Studies, The Animal Health Trust, Lanwades Park, Kentford, Suffolk CB8 7UU, UK. Fig 1: Ulcerated mass dorsal pastern. EQUINE VETERINARY EDUCATION / AE / JANUARY 2009 5 was not cleaned of faecal material. The gelding had been in the owner’s possession for 5 years, and was not known to have been imported or to have travelled abroad. a) Fig 4a: Habronema microstoma nematode in longitudinal section (arrow) within area of necrosis. Haematoxylin and eosin. b) Fig 4b: Habronema microstoma nematodes seen in longitudinal (white arrow) and transverse sections (black arrow), within area of necrosis. Haematoxylin and eosin. Fig 2: a) Latero-medial and b) Dorso-palmar weightbearing radiographic views revealing radiopaque areas within mass dorsal pastern. Fig 3: Surgical removal of mass. Note yellow ‘sulphur’ granules deep to the skin surface. Fig 5: Surgical wound 3 weeks post initial cast removal. 6 EQUINE VETERINARY EDUCATION / AE / JANUARY 2009 Clinical findings held in place with a layer of elasticated, nonadhesive bandage (Vetrap)7. Elasticated, adhesive bandage At presentation, the gelding was in good bodily condition. (Tensoplast)8 was used to fix the bandage proximally and All clinical parameters were within normal limits. A large distally to the skin and hoof capsule. The bandage was ulcerated mass, measuring 73 x 53 x 55 mm was present on changed b.i.d. for 3 days following surgery, decreasing to the dorsal pastern of the right foreleg. Palpation of the s.i.d. on Day 4 post surgery. Hydrogel (IntraSite)4 was mass was resented, and the mass was considered to be placed over the granulation bed prior to dressing adherent to the underlying tissue. No lameness was seen placement post surgery. From Day 7 post surgery bandage at the walk or trot. changes were every 2–4 days as necessary. For cost reasons the nonadhesive absorbent dressing (Allevyn) was Further investigation replaced with nappies (Pampers)9 and the secondary and tertiary layers reduced. This was continued until Week 8 Routine haematological examination, including a blood post surgery. smear, was unremarkable. Multiple radiographic views Antimicrobial (3 days of crystalline penicillin 10 Mu were obtained of the pastern region, which revealed no q.i.d., 6.6 mg/kg bwt gentamicin s.i.d.) and nonsteroidal involvement of deeper bony structures. The proximity of anti-inflammatory therapy (1 g b.i.d. for 3 days, followed the mass to the proximal interphalangeal joint (PIP) and by 1 g s.i.d. for 7 days) was continued post surgery. dorsal pouch of the distal interphalangeal joint (DIP) was Antimicrobial therapy was then changed to trimethoprim noted. The soft tissue structure of the mass was readily and sulphadiazine (Trimediazine, 5.2 mg/kg bwt visible, and seen to contain multiple radiopaque trimethoprim and 26 mg/kg bwt sulphadiazine per os)10 ‘granules’ (Fig 2). Ultrasonography of the mass showed for the following 21 days. Oral moxidectin paste areas of hyperechogenicity from 1–3 cm distal to the skin (Equest)11 was given 5 days post surgery at a dose rate of surface. The medial collateral ligament of the distal 0.4 mg/kg bwt. interphalangeal joint, the dorsmedial aspect of the distal The surgical site was skin grafted with punch grafts interphalangeal joint and extensor process of the third taken from the superficial pectoral muscles 17 and 27 days phalanx were visible and appeared uninvolved. The PIP post surgery to enhance healing by secondary intention. joint and associated structures were nonvisible The gelding responded poorly to bandage placement, ultrasonographically due to the position of the mass. resulting in self-mutilation secondary to multiple bandage displacements. The granulation tissue was therefore Differential diagnosis debrided and the foot and pastern cast at Weeks 8, 12 and 16 post surgery to allow epithelialisation. On consideration of the clinical and imaging findings, the principle differential diagnoses included a fibroblastic Histopathology sarcoid, a bacterial/fungal granuloma, exuberant granulation tissue, an eosinophilic granuloma, neoplasia, a The gross appearance was that of an ulcerated, firm foreign body reaction and cutaneous habronemaiasis. mass. Multiple yellow granules were seen within fibrous- type tissue. Histological examination showed a densely Treatment cellular mass within the dermis, extending to the surface of the skin. The mass consisted of sheets of eosinophils In view of the size of the mass, it was decided to attempt and mast cells along with fewer lymphocytes separated complete surgical excision under general anaesthesia into multiple variably sized lobules by prominent rather than biopsy the mass (Fig 3). Antimicrobial therapy trabeculae and organised collagen and fibroblasts. of crystalline penicillin (Crystapen, 10 Mu i.v.)1 and Within the mass were multiple variably sized areas of gentamicin (Gentaject 10%, 6.6 mg/kg bwt i.v.)2 and numerous degenerative neutrophils and eosinophils anti-inflammatory and analgesic therapy of depicting necrosis. Some sections showed single phenylbutazone (Equipalazone, 4.4 mg/kg bwt i.v.)3 was nematode larvae, measuring approximately 50 µm in given prior to surgery. The mass was removed with sharp diameter within the centre of these necrotic areas (Fig 4). excision without damaging any tendinous structures or Where intact, the epidermis was moderately penetration of the underlying PIP joint capsule. The hyperkeratotic and hyperplastic. margins of the surgical site were undermined to ensure removal of associated fibrous material. Primary closure Further diagnostics could not be achieved due to the large size of the defect and the tissue bed was left open for healing by To further classify the nematode larvae found on secondary intention histopathology, formalin fixed and paraffin embedded The granulation bed was dressed with a nonadherent, tissue was sent to a laboratory to undergo a novel semi- dry absorbent dressing (Allevyn)4 followed with a layer of nested PCR assay (Traversa 2004a,b, 2006, 2007). The tissue cotton wool5 and gauze (K Band)6 bandages. This was was PCR positive for H. microstoma. EQUINE VETERINARY EDUCATION / AE / JANUARY 2009 7 Outcome larvae do not complete their life cycle and can only survive up to one month in cutaneous tissue (Waddell The horse responded well to foot casts, which were 1969). The mechanism of stimulation of the exuberant managed at home under the guidance of the referring granulation tissue is unknown, but is thought to be a veterinary surgeon. Each cast was removed 3 weeks post hypersensitivity reaction to dead or dying larvae (von placement. This revealed a markedly decreased area of Tscharner et al. 2000). It is also suggested that the release granulation tissue, which at Week 16 (Fig 5) was smooth, of chemotactic factors from the larvae due to level, nonmalodorous and without discharge.