Reports of associations between APD and thyroid disease are even more infrequent than reports of APD and liver disease. Faver et al11 reported 3 cases of APD associated with hypothyroidism; 2 of these patients had concomitant diabetes mellitus. Although reports of associations between APD and thyroid disease are rare, it is unclear if this is because of a true rarity of coincidence or because the thyroid status of these patients typically is not checked or reported.
The pathogenesis of APD is unknown. The prominent association of APD with the symptom of pruritus has led many authors to speculate on a connection between scratching, trauma, and APD.3,18 Some studies have demonstrated increased expression of the 67-kD elastin receptor in lesions of perforating dermatoses; however, this expression is not uniformly elevated and the significance of this expression is not known.17 Other studies have found elevated levels of the extracellular matrix protein fibronectin in lesions of APD, but similar to the elastin receptor findings, the significance of this observation is unknown.19,20
Histopathologically, lesions of APD are characterized by acanthosis and focal vacuolar alteration in the basal epidermis, with an associated underlying mixed infiltrate of lymphocytes, macrophages, neutrophils, and occasional mast cells. A transepidermal canal can be identified that often contains parakeratotic keratin, degenerated inflammatory cells, elastin, and collagen. The elastin and collagen in these lesions appear normal ultrastructurally, and results of direct immunofluorescence studies are negative.21,22 In one study of APD associated with diabetes mellitus and renal insufficiency, needlelike crystals with some degree of calcification were identified. They were postulated to be uric acid or calcium hydroxyapatite crystals.23
Treatment of APD has proven to be challenging. Some clinicians report improvement of APD with topical retinoids19,24,25; topical, intralesional, or systemic corticosteroids26; oral doxycycline27; oral thalidomide9; oral allopurinol28; psoralen plus UVA phototherapy29; and broadband UVB phototherapy.11,30 Reports of narrowband UVB phototherapy in the treatment of APD appear promising.31,32 Ohe et al33 reported a case series of 5 patients with APD; all patients responded to narrowband UVB phototherapy.