Septic tenosynovitis in horses: 25 cases (1983-1989).

The medical records of 25 horses with septic tenosynovitis treated over 7 years (1983 to 1989) were reviewed to determine clinical features of the disease and response to treatment. The median age of horses with septic tenosynovitis was 5 years (range, 1 month to 21 years). Fourteen fore limbs and 11 hind limbs were affected. Sepsis was located in the sheath of the digital flexor tendons of 22 horses. Sepsis was located in the sheath of the extensor carpi radialis tendon (1 horse), sheath of the long digital extensor tendon (1 horse), or sheath of the common digital extensor tendon (1 horse) in the remaining horses. Nine horses received only medical treatment, using a combination of broad-spectrum parenterally administered antimicrobial drugs (8 of 9 horses), nonsteroidal anti-inflammatory drugs (8 of 9 horses), or irrigation of the wound (4 of 9 horses). Fourteen horses were treated surgically with either transection of the palmar/plantar annular ligament of the metacarpo/metatarsophalangeal joint (5 of 14 horses), lavage of the sheath after insertion of drains into the sheath (7 of 14 horses), or both (2 of 14 horses). All horses treated surgically were concurrently treated parenterally with broad-spectrum antimicrobial drugs and nonsteroidal anti-inflammatory drugs. Two horses with septic tenosynovitis were not treated and were euthanatized at the owners' request. Five horses were euthanatized before discharge from the hospital. Two horses (both treated medically) were lost to follow-up. Follow-up information was obtained for 18 horses, 6 to 55 months after discharge from the hospital.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tenoscopic-assisted treatment of open digital flexor tendon sheath injuries in horses: 20 cases (1992-2001)

OBJECTIVE: To determine history, physical and diagnostic examination findings, medical treatment, and outcome of horses with open injuries to the digital flexor tendon sheath treated with the assistance of tenoscopy. DESIGN: Betrospective study. ANIMALS: 20 horses. PROCEDURE: Medical records of 20 horses with open injuries to the digital flexor tendon sheath were reviewed. Signalment, history, physical and diagnostic examination results, bacteriologic culture and susceptibility testing results, surgical and medical treatments, and follow-up examination results were determined. Outcome was determined by use of telephone interview or physical examination. RESULTS: All horses were treated with tenoscopic-assisted lavage and debridement. Eighteen horses survived, and 2 were euthanatized during treatment. All horses were either grade-4 or grade-5 lame before treatment. Ten horses returned to previous use. Four horses were considered mildly lame and in athletic use. Three horses were considered mechanically lame and are in use with reduced expectations. One horse was lost to follow-up after being sold. One horse was euthanatized for financial reasons and 1 because of complications from regional sepsis. CONCLUSIONS AND CLINICAL RELEVANCE: Tenoscopy appears to be a useful modality in the treatment of open injury to the digital flexor tendon sheath in horses. Direct viewing, guided debridement, and targeted large-volume lavage are advantages obtained with intrathecal arthroscopy. Tenoscopy, when combined with antimicrobial and anti-inflammatory treatment, appears to offer a good chance of survival for affected horses.     

Treatment and outcome of chronic tenosynovitis in three horses

Three horses were presented for treatment of chronic infections of the digital flexor tendon sheath. Clinical signs included severe lameness, and heat, pain and swelling of the digital flexor tendon sheath. The horses were treated with surgical lavage of the tendon sheath, systemic and local antibiotics, and analgesics. In each case, resolution of the lameness occurred over weeks to months. Only one horse returned to athletic activity, while the other two became comfortable at pasture. Response to treatment in cases of chronic tenosynovitis may not be as rapid or complete as that reported for acute tendon sheath infections.     

Treatment and outcome of chronic septic tenosynovitis in three horses

Three horses were presented for treatment of chronic infections of the digital flexor tendon sheath. Clinical signs included severe lameness, and heat, pain and swelling of the digital flexor tendon sheath. The horses were treated with surgical lavage of the tendon sheath, systemic and local antibiotics, and analgesics. In each case, resolution of the lameness occurred over weeks to months. Only one horse returned to athletic activity, while the other two became comfortable at pasture. Response to treatment in cases of chronic tenosynovitis may not be as rapid or complete as that reported for acute tendon sheath infections.     

Traumatic Septic Tenosynovitis of the Tarsal Sheath with Fragmentation of the Sustentaculum Tali: Surgical Treatment and Outcome in 3 Horses

This case report describes surgical treatment of 3 cases of septic chronic tenosynovitis of the tarsal sheath with fragmentation of the sustentaculum tali in 3 horses. Diagnosis was based on clinical signs, radiographic and ultrasonographic findings, synovial fluid cytology, and bacteriology. In each case, treatment consisted of tenovaginoscopy of the tarsal sheath performed with the horse under general anesthesia and regional intravenous perfusion of antibiotics. Follow-up data obtained between 12 and 46 months after surgery reported a good outcome, with a good cosmetic appearance in all cases described. Two horses returned to their intended use at 44 and 46 months, and 1 horse reportedly showed a remarkable functional improvement after 12 months. Despite the poor prognosis associated with the chronicity of the lesions, the presence of adhesions and the degree of involvement of the lateral digital flexor tendon, tenovaginoscopy of the tarsal sheath and regional antimicrobial therapy were successful therapeutic options for treating septic tenosynovitis of the tarsal sheath with fragmentation of the sustentaculum tali.     

CLINICAL AND DIAGNOSTIC IMAGING CHARACTERISTICS OF LATERAL DIGITAL FLEXOR TENDINITIS WITHIN THE TARSAL SHEATH IN FOUR HORSES

Lateral digital flexor tendonitis is a rarely reported cause of hind limb lameness in performance horses. The purpose of this retrospective study was to describe clinical and diagnostic imaging findings for a group of horses with lateral digital flexor tendinitis within the tarsal sheath. Equine cases with a diagnosis of lateral digital flexor tendonitis and magnetic resonance imaging (MRI) studies of the affected region were retrieved from North Carolina University's medical record database. Recorded data for included horses were signalment; findings from history, physical examination, lameness examination, and all diagnostic imaging studies; treatment administered; and outcome. Four horses met inclusion criteria. Lameness was mild/moderate in severity and insidious in onset in all patients. Responses to flexion tests were variable. All horses showed positive improvement (70–90%) in lameness after tarsal sheath analgesia. Radiographic, scintigraphic, and ultrasonographic findings were inconclusive. For all horses, MRI characteristics included increased T2, PD, and STIR signal intensity within the lateral digital flexor tendon in the area of the tarsal sheath. Tarsal sheath effusion was slight in three horses, and mild/moderate in one horse. With medical treatment, two horses were sound at 6‐month followup, one horse was sound at 1‐year followup, and one horse had a slight persistent lameness (grade 1/5) at 9‐month followup. Findings supported the use of MRI for diagnosing lateral digital flexor tendonitis within the tarsal sheath in horses. Affected horses may have a good prognosis for return to athletic performance following appropriate medical treatment.     

Treatment of septic common digital extensor tenosynovitis by complete resection in seven horses

OBJECTIVE: To describe and evaluate a technique for radical resection of the entire intrathecal component of the common digital extensor tendon (CDET) in horses. STUDY DESIGN: Prospective clinical study. ANIMALS OR SAMPLE POPULATION: Seven client-owned horses. METHODS: Seven horses with wounds that resulted in septic tenosynovitis of the CDET sheath were treated by complete surgical resection of the affected tendon and ablation of the tendon sheath; 5 had previous surgery that was unsuccessful. Time from initial injury to complete resection was 1-22 weeks. In 6 horses, the wound was closed primarily using a closed suction (4 horses), penrose (1), or passive open drainage system (1). In 1 horse, the surgical wound healed by second intention. All horses had postoperative bandaging, antibiotic administration, and physiotherapy. RESULTS: Surgical wounds healed primarily in 6 horses and by second intention in 1 horse. Follow-up (mean, 26.4 months; range, 18-38 months) was available for 6 horses; all returned to their athletic performance level without lameness or gait abnormality. CONCLUSIONS: Complete resection of the CDET was an effective surgical technique for management of chronic septic tenosynovitis. CLINICAL RELEVANCE: Horses with infection of the CDET and its sheath may be returned to long-term soundness without gait abnormality after radical resection.     

Closed Suction Drainage in the Treatment of Infectious Arthritis of the Equine Tarsocrural Joint

Infectious arthritis of the tarsocrural joint was treated in 13 horses with closed suction drainage through a flat, fenestrated, latex (Jackson-Pratt) drain, broad-spectrum antimicrobial agents, nonsteroidal anti-inflammatory drugs, and bandage immobilization. In 11 horses, arthroscopic lavage and debridement were also performed. Ingress drains were placed for lavage in six horses. Ten horses returned to their previous level of competition or were sound. One horse raced but had lameness of the affected tarsocrural joint and dropped in racing class; one horse was euthanatized because of laminitis in the supporting limb; and one horse was lame, but useful as a breeding animal. Closed suction drainage appeared to be a useful treatment in horses with infectious arthritis. Although arthroscopy was not necessary, it facilitated fibrin removal, lavage, and partial synovectomy. Because of the development of Pseudomonas superinfection in one horse, the use of simultaneous ingress catheters was not recommended.     

Occult subchondral osseous cyst-like lesions of the equine tarsocrural joint

OBJECTIVE: To report the clinical signs, diagnosis, management, and outcome of horses with occult sub-chondral osseous cyst-like lesions of the tarsocrural joint. DESIGN: Retrospective study. ANIMALS: Twelve horses with subchondral osseous cyst-like lesions (SOCLs) in the tarsocrural joint. METHODS: Information about history, examination findings, diagnostic techniques, and surgical procedures as obtained from medical records. Outcome was determined by patient re-evaluation and telephone communication with the referring veterinarian, owner, or trainer. RESULTS: Horses were aged from 3 to 29 years. Lameness (2 weeks to 1 year) varied from moderate to severe. Synovial fluid analyses (9 horses) yielded changes consistent with suppurative inflammation and positive bacterial culture was obtained in 4 horses. Eight of 9 horses that had intra-articular analgesia had a dramatic reduction in lameness. No abnormalities were detected on tarsal radiographs in 10 horses. Scintigraphy identified foci of increased radiopharmaceutical uptake in the distal tibia or talus of all horses, and the lesion was further characterized by computed tomography in 7 horses. SOCLs were identified in the medial malleolus (5), intertrochlear groove of the talus (4), lateral malleolus (2), and distal intermediate ridge of the tibia (1). One horse was euthanatized, 6 horses had surgical debridement, and 5 horses were managed conservatively. Four horses treated surgically (67%) returned to soundness. Conservatively treated horses continued to exhibit lameness but 2 were sufficiently sound for light pleasure riding. CONCLUSIONS: Occult lesions of the tarsus not visible on radiographs can be detected by computed tomography and scintigraphy and may be a source of lameness. CLINICAL RELEVANCE: SOCL, possibly of septic origin, should be a differential diagnosis for persistent lameness localized to the tarsocrural joint without radiographic abnormalities. Surgical debridement of the lesions may offer the best prognosis for a return to athletic soundness.     

Exostoses of the caudal perimeter of the radial physis as a cause of carpal synovial sheath tenosynovitis and lameness in horses: 10 cases (1999-2003)

OBJECTIVE: To determine the clinical, radiographic, ultrasonographic, and arthroscopic findings associated with tenosynovitis of the carpal synovial sheath induced by exostoses that originate from the caudal surface of the physeal scar of the distal radius and determine the results of surgical removal of those exostoses in horses. DESIGN: Retrospective study. ANIMALS: 10 horses. PROCEDURE: Medical records of horses with effusion in the carpal synovial sheath and lameness evaluated from 1999 to 2003 were examined. RESULTS: All horses had a history of intermittent mild to moderate effusion of the carpal synovial sheath and lameness of 1 forelimb. Results of regional perineural and intrathecal anesthesia of the carpal synovial sheath confirmed that the lameness originated in the carpal synovial sheath. Radiography revealed exostoses originating from the caudal cortex of the distal radius at the level of the closed physis. Arthroscopy was performed for confirmation and removal of exostoses that penetrated the carpal synovial sheath and impinged on the deep digital flexor tendon. All horses returned to previous athletic activity. One horse had a recurrence of clinical signs 12 months after surgery, which resolved with medical treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Tenosynovitis of the carpal synovial sheath and lameness were caused by impingement of exostoses of the caudal radius on the lining and contents of the carpal synovial sheath. Although the clinical signs and surgical treatment were similar to that caused by osteochondromas, these exostoses developed at the level of the closed physis of the distal radius and were not radiographically or histologically similar to osteochondromas.     

Tenoscopic removal of a protruding osteophyte as a treatment for chronic common digital extensor tendinopathy and associated tenosynovitis

This report describes an adult Quarter Horse gelding that was presented for evaluation of chronic tenosynovitis of the right common digital extensor tendon sheath. Radiographic and tenoscopic evaluation confirmed the presence of a periarticular osteophyte from the third metacarpal bone protruding into the common digital extensor tendon sheath. Tenoscopic surgical resection of the osteophyte and debridement of the affected tendon resolved the tenosynovitis and associated right forelimb lameness. Osteophytes in this location can be a source of focal traumatic tendonitis of the common digital extensor tendon which can lead to a chronic tenosynovitis of the common digital extensor tendon sheath. Tenoscopic debridement and lavage is a viable treatment option for chronic nonseptic common digital extensor tendinopathy and associated tenosynovitis.     

Surgical treatment of tarsal sheath effusion associated with an exostosis on the calcaneus of a horse

A 2-year-old Thoroughbred colt was referred for evaluation of effusion within the tarsal sheath and associated lameness of the right hind limb. Conservative treatment consisting of needle aspiration and pressure bandaging had been unsuccessful. Radiography of the right tarsus revealed proliferative periosteal reaction along the distal caudal border of the sustentaculum tali and medial aspect of the calcaneus. The owners elected conservative treatment, using a local injection of corticosteroid and pressure bandaging the tarsus. Five months later, the severity of the effusion and lameness had increased. Radiography revealed increased reactive bone along the sustentaculum tali and mineralization of the plantar tarsal ligament and tarsal sheath. Surgical exploration revealed fibrous adhesions between the medial aspect of the calcaneus and the flexor tendon and associated soft tissue mineralization. The adhesions were broken down and the reactive bone along the calcaneus was removed. The mineralized soft tissue within the tarsal sheath was excised. Five months after surgery, the horse was sound at the trot, with only minimal tarsal sheath effusion. The response to treatment for tarsal sheath effusion and lameness caused by bony changes of the sustentaculum tali is often unsatisfactory. After responding poorly to conservative treatment, the horse in this report had a favorable outcome to the surgical intervention of this condition.     

Osteomyelitis of the calcaneus in horses: 28 cases (1972-1987)

Medical records of 28 horses with osteomyelitis of the calcaneus were reviewed to evaluate signalment, history, diagnostic and treatment methods, outcome, and long-term follow-up information. Trauma was the most commonly reported cause (24). Physical examination revealed lameness in 27 horses, and 22 (79%) had a wound or draining tract over the plantar aspect of the calcaneus. Radiography of all horses was done prior to the initiation of treatment, and follow-up radiography was done on 20 horses. The most common radiographic findings were soft tissue swelling (25), bony lysis of the calcaneus (17), bone fragments or sequestra from the tuber calcis (13), and periosteal new bone production or bony lysis of the sustentaculum tali (5). Association could not be found between initial radiographic findings and eventual outcome of the case. Positive bacterial cultures were obtained from 13 horses. A wide variety of gram-positive, gram-negative, and anaerobic organisms were isolated. Fourteen of the 15 isolates, for which susceptibilities were reported, were susceptible to penicillin, gentamicin, or trimethoprim sulfamethoxazole. Twenty-six of the 28 horses diagnosed as having osteomyelitis of the calcaneus were treated; 16 horses were treated with surgical debridement in addition to antimicrobial treatment, and 10 horses were treated with antimicrobial agents, anti-inflammatory drugs, or supportive wound care. There was no significant difference in survival rate of horses treated surgically and those treated conservatively. Six horses that were treated were later euthanatized for problems associated with chronic osteomyelitis, and 2 horses died or were euthanatized for unrelated problems. Eighteen horses (64%) were alive at last follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)     

Unilateral distension of the tarsal sheath in the horse: a report of 11 cases

Eleven horses with unilateral distension of the sheath are reported with emphasis on the use of plain and contrast radiography in diagnosis. Six had associated bony abnormalities of the sustentaculum tali, and two of these showed destructive or mixed destructive and proliferative lesions resulting from osteomyelitis. One horse had a fracture of the sustentaculum. In three horses proliferative changes were found. Bony changes were best demonstrated on a dorsomedial-plantarolateral oblique view. Contrast radiography of the tarsal sheath was performed in five cases without, and two horses with, associated bony lesions. In five cases ballooning with or without folding of the proximal aspect of the sheath was demonstrated. Additional band-like filling defects (two cases), triangular filling defect (one case), nodular intra-tendovaginal masses (two cases), or an extra-tendovaginal mass (one case) were noticed. The remaining two horses showed a semicircular collar shape dilation of the proximal aspect of the sheath. Contrast radiography appeared to be a helpful tool for the examination of tarsal sheath lesions. Two horses with associated bony changes were destroyed immediately after diagnosis, one failed to recover following surgical intervention and in three horses the outcome was unsatisfactory after conservative treatment. Three horses without associated bony lesions recovered completely after conservative treatment. One was operated on subsequently; the results are promising but the outcome of this case is not yet known. One was sold shortly after diagnosis and lost to follow up.     

Osteolytic lesions of the tuber calcanei in two horses

Two adult horses were evaluated for chronic hind limb lameness. Nonseptic calcanean bursitis with associated focal osteolytic lesions at the point of insertion of the gastrocnemius tendon was diagnosed in each horse by physical and lameness examinations, radiography, ultrasonography, and synovial fluid analysis. Both horses underwent arthroscopic exploration and lavage of the affected bursa, and one horse also underwent surgical debridement of the osseous lesion. Both horses remained lame for 13 months after the surgical procedures. To our knowledge, osseous lesions of the calcaneus in horses with nonseptic calcanean bursitis have not been reported. The flexed proximoplantar-to-distoplantar tangential radiographic view of the calcaneus was essential in localizing the lesions, as was the sonogram in one horse. Arthroscopy provided a thorough evaluation of the bursa and associated tendons. On the basis of the outcome of these 2 horses, the prognosis for complete recovery for horses with this condition appears to be unfavorable. Surgical debridement of the osseous lesion was of no benefit and may have been detrimental.     

Destructive lesions of the proximal sesamoid bones as a complication of dorsal metatarsal artery catheterization in three horses

OBJECTIVE: To describe focal destructive lesions of the proximal sesamoid bones (PSBs) as a complication of dorsal metatarsal artery catheterization performed for direct blood pressure monitoring during equine general anesthesia. STUDY DESIGN: Retrospective study. ANIMALS: Three client-owned horses. METHODS: A dorsal metatarsal artery was catheterized in each of 3 horses for direct blood pressure monitoring during anesthesia. Radiography, ultrasonography, synoviocentesis, and arthroscopy were used to diagnose postoperative lameness that occurred in the limb used for blood pressure monitoring. RESULTS: Horses developed severe lameness, localized to the fetlock region of the catheterized limb within 21 days of surgery. Antibiotic therapy was administered. Surgical debridement was possible in 1 horse. Two horses that had lesions that were inaccessible, failed to respond to medical management and were euthanatized. The 3rd horse that had surgical debridement of affected bone, survived. Changes in hospital protocol, by improving aseptic technique during catheter insertion and use of new manometer tubing and heparinized saline for each arterial catheter inserted in the dorsal metatarsal artery, have eliminated this complication. CONCLUSIONS: Diagnosis and treatment of destructive lesions of the PSB were difficult. Strict aseptic technique should be followed during insertion of arterial catheters. CLINICAL RELEVANCE: Focal destructive lesions of the PSB subsequent to dorsal metatarsal arterial catheterization is a rare but serious complication of equine anesthesia.     

Intrathecal deep digital flexor tenectomy for treatment of septic tendonitis/tenosynovitis in four horses

Objective: To describe partial removal of the intrathecal component of the deep digital flexor tendon (DDFT) in horses with chronic septic DDF tendonitis and tenosynovitis unresponsive to conventional therapy, and to report long‐term outcome. Study Design: Case series. Animals: Horses (n=4). Methods: Four horses with chronic septic DDF tendonitis and tenosynovitis were treated by surgical tenectomy of the intrathecal component of the DDFT, followed by stabilization in casts and subsequent corrective shoeing. All horses were previously managed unsuccessfully with combinations of conventional therapy consisting of systemic antibiotics, through and through tendon sheath lavage/open drainage, regional limb perfusions, tenoscopy with debridement and transection of the palmar/plantar annular ligament, and intrathecal antibiotics. Results: Time from initial injury/diagnosis to tenectomy ranged from 10 to 210 days. Mean hospitalization time after surgery was 82 days. Long‐term follow‐up (>1.5 years; mean, 3.8 years) was available. All 4 horses were able to walk comfortably at pasture and were used as broodmares. Conclusions: Intrathecal tenectomy is a viable surgical procedure for treatment of chronic septic tenosynovitis of the digital sheath that is complicated by septic tendonitis of the DDFT.     

Arthroscopic treatment of meniscal cysts in the horse

Reasons for performing study: To describe the clinical symptoms, treatment, and outcome of meniscal cysts in horses. These structures have not been previously described in the literature as a potential cause of lameness in the horse. Hypothesis: Meniscal cysts are an uncommon condition of the femorotibial joint but can be a significant cause of lameness. Symptoms can be resolved by arthroscopic excision. Methods: Records of horses diagnosed with meniscal cysts and treated by cyst excision and meniscal debridement at 2 surgical practices were reviewed. Clinical outcome was determined by repeat veterinary examination and contact with owner. Results: Seven cases of meniscal cyst were treated with arthroscopic cyst excision and meniscal debridement. Five of 7 horses had lameness attributable to femorotibial joint pathology, while the remaining 2 horses had meniscal cysts found incidentally during diagnostic arthroscopy for the treatment of osteochondritis dissecans of the lateral trochlear ridge of the femur. Five of 6 horses with long‐term follow‐up were sound and a 7th horse was improved 11 months after surgery. Conclusions and potential relevance: Meniscal cysts, while uncommon, can be associated with progressive lameness in the horse. Surgical excision of the cysts results in resolution or improvement of symptoms, without evidence of recurrence on follow‐up examination.     

Heel bulb lacerations in horses: 101 cases (1988-1994)

OBJECTIVE: To determine clinical history, structures involved, treatment, and outcome of lacerations of the heel bulb and proximal phalangeal region (pastern) in horses. DESIGN: Retrospective study. ANIMALS: 101 horses. PROCEDURES: Medical records of horses with lacerations of the heel bulb and pastern were reviewed, and follow-up information was obtained. RESULTS: 75 horses were Quarter Horses. Most horses were not treated with antimicrobial drugs prior to referral. Mean +/- SD time from injury to referral was 24 +/- 45 hours (range, 1 to 168 hours). Lacerations were most frequently caused by contact with wire or metal objects. In 17 horses, lacerations involved synovial structures; the distal interphalangeal joint was most commonly affected. One horse was euthanatized after initial examination. Wound treatment consisted of cleansing, lavage, debridement, lavage of affected synovial structures, suturing of fresh wounds, and application of a foot bandage or cast. Fifty-six horses were treated with systemically administered antimicrobial drugs. Follow-up information was collected for 61 horses. Fifty-one horses returned to their intended use and had no further complications; 10 horses had complications associated with the wound, and of those horses, 5 were euthanatized and 1 horse died from an unrelated cause. Horses with lacerations that involved synovial structures had worse outcomes than horses with lacerations that did not involve synovial structures. CONCLUSIONS AND CLINICAL RELEVANCE: Horses that sustain heel bulb lacerations can successfully return to their intended use. Involvement of the distal interphalangeal joint is associated with poor prognosis.     

Mastocytoma in the common carpal sheath of the digital flexor tendons of a horse

A 13-year-old Morgan gelding was examined for right forelimb lameness and tenosynovitis of the right common carpal sheath of the digital flexor tendons. The horse had moderate right forelimb lameness at the trot and marked effusion of the right common carpal sheath of the digital flexor tendons. Ultrasonographic examination revealed a soft tissue mass within the proximal pouch of the affected tendon sheath, located adjacent to the distal physis of the radius. Cytology and culture of the fluid revealed a sterile, eosinophilic tenosynovitis. Tenoscopic exploration confirmed the presence of a capsulated soft tissue mass. Thecotomy was required to fully debride the mass, which histology revealed to be a mast cell tumour. At 22 months postoperatively, the horse developed mild right forelimb lameness and eosinophilic tenosynovitis because of recurrence of the mastocytoma. Mastocytosis is a possible differential diagnosis in any horse exhibiting lameness associated with tenosynovitis. Surgical excision combined with rest and postoperative intrasynovial and systemic corticosteroids may be palliative.