Page 376 - The Vasculitides, Volume 1: General Considerations and Systemic Vasculitis

350 Sarah Conway and David S. Younger

but Goldmann perimetry showed residual central visual field defect [115]. Central retinal
artery occlusion generally carries a less favorable prognosis.

Microscopic Polyangiitis

This necrotizing small vessel vasculitis typically affects the kidney causing a pauci-
immune focal necrotizing crescentic glomerulonephritis, and the lungs causing pulmonary
capillaritis. Its annual incidence is 3.6 cases per million people [124], with a mean age of
onset over 50 years, and slightly male predominance with a male to female ratio varying from
1 to 1.2:1 [62, 125]. The histopathology of MPA is similar to GPA and EGPA in that there is
a necrotizing vasculitis; however, the absence of granulomatous inflammation distinguishes
MPA from GPA, as does absence of asthma and eosinophilia from EGPA [126].

In 1990 the ACR developed criteria for diagnosing the systemic vasculitides, but it did
not distinguish MPA from PAN. However, the 2012 revised CHCC distinguished the two
defining MPA as a necrotizing vasculitis, with few or no immune deposits, predominantly
affecting small vessels, often associated with necrotizing glomerulonephritis and pulmonary
capillaritis; granulomatous inflammation is absent [3]. Although the presence of ANCA is not
part of the diagnostic criteria, up to 65% of patients are positive for pANCA [125, 127].

Ocular findings are not part of the diagnostic criteria for MPA, and are much less
common in MPA than in other AAV. Nevertheless, ocular involvement can occur in up to
24% of patients with MPA most often presenting as episcleritis or conjunctivitis [128]. A
study by Rothschild and colleagues [62] in 280 patients with MPA found that 25 (9%) had
ocular manifestations. Of those with ocular manifestations, the most common was
conjunctivitis occurring in 7 (28%), episcleritis occurring in 5 (20%), and blurred vision
occurring in 4 (16%). Other less frequent ocular manifestations included retinal vasculitis in 3
(12%), retinal exudates, optic neuropathy, sudden visual loss and oculomotor nerve palsy in 2
(8%) patients each, and scleritis, keratitis, uveitis, retinal hemorrhage in 1 patient (4%) each.
Other studies report less frequent ocular manifestations of disease, so noted in a study by
Guillevin and colleagues [125] in a study of 85 patients that found only 1 patient (1.2%) with
ocular involvement.

Although ocular signs and symptoms are rarely presenting features of MPA, there are
patients who initially present with ocular involvement. Hara and colleagues [127] described a
patient who presented with hyperemia and photophobia of the eyes and found to have limbal
infiltration, iritis and scleritis due to MPA. Altaie and co-workers [129] reported an 80-year-
old woman with MPA who presented with painless vision loss in the right eye, and was found
to have optic neuritis. Darlington and co-workers [130] described a 16-year-old woman with
the initial presentation of peripheral keratitis.

Episcleritis and conjunctivitis are the commonest ocular manifestations of MPA, and it is
critical to distinguish between the two since episcleritis generally implies a worse prognosis.
Alrashidi and colleagues [131] demonstrated the importance of recognizing anterior scleritis
in the description of a patient with MPA with recurrent episodes of pain and redness for 7
years thought to be due to conjunctivitis. Eventually, the patient was diagnosed with
episcleritis when she presented with severe ocular inflammation and vision loss, and slit lamp
evaluation that demonstrated episcleritis. Thus, the authors suggest that a slit lamp evaluation

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