What workup do you do for patients who have PL-7 elevation when screening for myopathy?

In the literature, the PL-7 antibody has been associated with the antisynthetase syndrome and aside from myositis, interstitial lung disease (ILD). Patients with PL-7 autoantibodies are at high risk of ILD. Referral to pulmonary should be considered. One would also consider assessing pulmonary function (including DLCO)  and a high-resolution CT scan of the chest. 

I agree completely with Dr. @Dr. First Last: PL-7+ patients may manifest any of the classic anti-synthethase syndrome (ARS) or dermatomyositis features, but several analyses have suggested that both PL-7+ and PL-12+ patients may have more significant ILD and more variable muscle involvement than Jo-1 or other ARS-associated myositis specific antibodies (i.e., Hervier et al., PMID 22771754; Pinal-Fernandez et al., PMID 28339994).

This has also been our experience at the Emory Myositis rheumatology clinic, though we may have a referral bias as many of these patients were initially identified/referred by our colleagues in the Emory ILD pulmonology clinic.

It's still debated whether ILD is more difficult to treat in patients with one type of ARS-associated myositis-specific antibodies than another but, given the hope that early treatment might help improve the natural history of the disease, I will typically much more routinely screen for the development of ILD in PL-7 or PL-12 patients who do not initially have lung involvement than I might in other antibody types.

Interestingly, some older literature also suggested an increased risk of pulmonary hypertension in PL-7+ ARS patients (which has been shown to worsen ARS mortality and morbidity). As such, I anecdotally will consider periodically checking screening echocardiograms on PL-7+ patients, esp. those who have ongoing/progressive dyspnea despite stable PFTs and CT imaging, or those who have markedly elevated FVC/DLCO ratios (analogous to the ratios reported in PAH from systemic sclerosis).