Chapter 7.2
Equine sarcoidosis: clinical signs, diagnosis, treatment and outcome of 22 cases
Background – Equine sarcoidosis may present as a generalized or localized exfoliative dermatitis and/or as a granulomatous inflammation of multiple organs.
Objectives – To report the clinical signs, diagnosis, treatment and outcome for 22 horses with histologically confirmed sarcoidosis.
Animals – Twenty-two horses of different breeds, between 3 and 17 years of age.
Methods – Diagnosis was based on clinical signs and histopathological findings.
Results – The following three forms of equine sarcoidosis were identified: generalized (13.6%), partially generalized (18.2%) and localized (68.2%). High-dose systemic corticosteroids were used as the initial treatment in all three forms, followed by lower doses for a variable number of weeks. No local treatment was prescribed. Case outcome was variable; one of three cases of generalized sarcoidosis was euthanized immediately and the remaining two were euthanized after 2–3 months of unsuccessful treatment; all four cases of partially generalized sarcoidosis deteriorated despite treatment and were euthanized after 3.5–12 months; two cases with localized disease showed no response or insufficient response to treatment and were euthanized; four cases recovered fully with or without treatment, and one showed partial recovery without treatment; and eight cases improved whilst receiving prednisolone but required continuous low doses to maintain remission.
Conclusions and clinical importance – Recognition of the different forms of sarcoidosis based on history, clinical appearance and histopathology assisted in making an informed choice between treatment and euthanasia and prevented unnecessary local treatment. Equine sarcoidosis should be included in the differential diagnosis of a localized exfoliative dermatitis of unknown origin.
Introduction
Equine sarcoidosis (ES) has also been referred to as ‘equine idiopathic granulomatous disease’, ‘equine generalized granulomatous disease’, ‘equine systemic granulomatous disease’, ‘equine histiocytic disease’ and ‘equine histiocytic dermatitis’.1–4
Equine sarcoidosis is a rare disease complex that initially may present as an exfoliative dermatitis or as a nodular form characterized by granulomatous inflammation of multiple organs.3–6 Both forms have similar outcomes; horses with exfoliative dermatitis frequently develop nodules, and horses with the nodular form will usually develop exfoliative dermatitis.4,5 Sarcoidosis can also be categorized into the following three clinical presentations based on disease extension: ‘generalized’, ‘partially generalized’ and ‘localized’. Peripheral lymphadenopathy may be present in the generalized and partially generalized presentations.3–5,7 The localized presentation tends to remain localized, without the development of systemic clinical signs.8 The onset of sarcoidosis may be insidious or rapid.2,4
The skin lesions are variable but mostly characterized by focal, multifocal or generalized scaling and crusting, with varying degrees of alopecia.2–4 Lesions are often well demarcated.3
In the generalized form, nodules may be found in order of decreasing frequency in the lungs, lymph nodes, liver, gastrointestinal tract, spleen, kidneys, bones and central nervous system.2–4 There may be serious skin involvement or no skin involvement.9 Most horses with generalized sarcoidosis develop a wasting syndrome characterized by one or more of the following clinical signs: exercise intolerance, increased respiratory rate at rest, mild dyspnoea, poor appetite, weight loss, ventral oedema, and persistent or fluctuating low-grade fever.2,4
No age or sex predilections have been recognized,2–5 although Spiegel et al.10 noted a predisposition for thoroughbreds and geldings. This was also described by Loewenstein et al.11 There is no documented seasonality.4,10 In contrast to human sarcoidosis, pruritus is rarely encountered in ES.3–6,10,12,13 There is no proven aetiology or causative agent, although many triggering factors have been suggested.2–4 In humans, it is believed that sarcoidosis may be an aberrant reaction to an infectious agent or an antigen, and this may also be true in the horse.2,7,14 Spiegel et al.10 could not identify any infectious aetiological agent, and these authors concluded that ES is unlikely to have a microbial aetiology. White et al.15 reported a failure in detecting DNA from equine herpesvirus 1 and 2 in paraffin-embedded skin of eight cases of ES, but these authors did not discount equine herpesvirus 1 or 2 as a cause in some cases. A putative causative role for Mycobacterium spp. has been proposed for human sarcoidosis, and was suggested in a single equine case.16
Most authors suggest that glucocorticoids are the therapy of choice.2,4,17 In addition to glucocorticoids, dietary ω3/ω6 fatty acids for at least 3–12 weeks (dosage depending on manufacturer) and pentoxifylline [10 mg/kg twice daily orally (p.o.)] may be used as adjunctive therapy, but the benefits have not been established.4 Dietary changes may be helpful, given that diseases similar or identical to ES have been caused by hairy vetch (Vicia villosa), and those horses responded to dietary changes.3,18
The prognosis for generalized sarcoidosis is poor,1,5,6,12 although some authors describe that weight gain may occur during glucocorticoid therapy and that euthanasia may not be required.19 Spontaneous resolution has also been reported.2,4
The aim of the present study was to report the clinical signs, diagnosis, treatment and outcomes for 22 horses with confirmed equine sarcoidosis seen between 2002 and 2011.
Materials and methods
The Animal Ethics Committee of Utrecht University concluded that this study did not require its approval because it was a patient-based study.
Horses
Twenty-two cases of ES were seen between 2002 and 2011. Twenty animals were referred to the Utrecht University clinic, and two were cases seen at the Utrecht University outpatient clinic. Information collected included the following: age, breed, sex, onset of clinical signs, distribution and type of skin lesions, diagnostic investigations, treatment and response to treatment.
Diagnosis
All horses were tentatively diagnosed with sarcoidosis (Figures 1,3,5,7 and 9) based on the characteristic of skin lesions (exfoliation, crusting alopecia, increased local skin temperature, subcutaneous oedema and/or nodule formation) and/or systemic signs (e.g. fever, weight loss, lymphadenopathy). The tentative diagnosis was confirmed by histological examination of skin biopsies (Figures 2,4,6,8 and 10) and/or other tissue biopsies (e.g. Tru-Cut needle biopsy) by a board-certified veterinary pathologist (G.C.M.G.). Patients were included in the study when the biopsies revealed a multifocal to diffuse lympho-granulomatous dermatitis with multinucleated giant cells.
Figure 1. Localized sarcoidosis: 13-year-old standardbred gelding (case 1) with crusting, scaling and hair loss on the right hindlimb.
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