Patients with plasma cell dyscrasias are capable of producing large amounts of free light chains [
1]. In patients without an excessive production of free light chains, most excess light chains are rapidly cleared from the serum by glomerular filtration, which results in either their reabsorption and destruction by tubular cells or their excretion in the urine [
2]. Occasionally, with plasma cell dyscrasias, the extremely large amount of free light chains produced can overwhelm the glomerular system, resulting in renal tubular damage and even overt renal failure [
1]. Light chain deposition disease (LCDD) itself is most often a systemic disorder resulting from an underlying plasma cell or B-cell neoplasm [
3]. LCDD is also often a diagnosis of exclusion, because amyloidosis must be ruled out by examination of fibrils for Congo red staining and apple green birefringence [
3]. LCDD affects men more commonly than women and most often presents in systemic cases with renal manifestations [
3]. Most extrarenal cases of systemic LCDD involve the heart, liver, and peripheral nervous system [
3]. Localized LCDD is rare. Most cases of isolated, or localized, LCDD involve the kidney and skin, and cases of isolated pulmonary LCDD are rare, with less than 50 reported cases available in the literature, which is impressive because this phenomenon was first described in 1988 [
4‐
6].
Of these rare cases of pulmonary LCDD, two separate histological patterns are appreciated—diffuse and nodular—with patients with nodular deposits having a better overall prognosis [
5,
7]. Nodular pulmonary LCDD often appears similar to nodular amyloidosis radiographically and clinically, with the presentation involving either solitary or multiple pulmonary nodules in an otherwise asymptomatic patient [
3]. These patients also often lack interstitial lung involvement that can be seen more commonly in systemic cases [
3]. Additionally, nodular pulmonary LCDD has been shown to be more frequently associated with an underlying plasma cell dyscrasia or renal failure than pulmonary amyloidosis, with about 50% of cases of nodular pulmonary LCDD associated with an underlying plasma cell disorder, a low-grade B-cell lymphoproliferative disorder, or, in rare cases, even Sjögren syndrome [
3,
5,
8]. Because our patient had monoclonal gammopathy of undetermined significance (MGUS), her diagnosis of nodular pulmonary LCDD fits within this small number of previously described cases.