Orbital myositis: a study of six cases.

Orbital myositis implies orbital inflammation confined to one or more of the extraocular muscles. Orbital computerised tomography (CT) demonstrates irregular extraocular muscle enlargement which extends anteriorly to involve the tendon (muscle insertion). Six cases of presumed orbital myositis are reported, in each of whom the diagnosis was suspected clinically and confirmed by the orbital CT scan appearances. The mean age of the patients was 33 years (range 8-45 years). All presented with painful ophthalmoplegia and the majority manifested proptosis (five cases), conjunctival congestion (five cases) and periorbital and eyelid edema (two cases). Systemic corticosteroid therapy was used in two patients initially and also in another patient who relapsed, with rapid and dramatic responses. Extraocular muscle biopsy was performed in one case, disclosing features of non-specific muscle inflammation and no evidence of vasculitis. It is considered that orbital myositis is a discrete, identifiable subgroup within the spectrum of the nonspecific idiopathic orbital inflammatory syndromes; termed previously orbital 'pseudotumours'. Although the clinical features are frequently suggestive, they are nonspecific, and non-invasive investigations such as orbital ultra-sonography and CT scanning are required for precise anatomical tissue localisation and diagnosis. The role of ocular muscle biopsy is probably limited to atypical cases, or those unresponsive to steroid therapy, particularly to exclude neoplasia. Orbital myositis may be acute, subacute or recurrent. The acute form responds well to high doses of oral corticosteroids tapered gradually, but it may recur or become chronic. The subacute form of the disease responds less well.