Presented by: Jing Zhang, MD and Carrie Ann Cusack, MD
Drexel University College of Medicine
May 16, 2014
Interstitial granulomatous dermatitis (IGD), a histopathologic reaction pattern, was first described by Ackerman in the early 1990s. It typically occurs in patients with autoimmune disorders with the inciting event thought to be immune complex deposition around small dermal blood vessels leading to collagen degeneration. The degenerated collagen causes an immune response, and it is thought that persistent levels of immune complexes may contribute to perpetuation of disease.
IGD is characterized by symmetric erythematous to violaceous papules and plaques on the trunk and extremities. The sites of predilection include the lateral chest wall and medial thighs. Additionally, linear indurated cord-like lesions referred to as the “rope sign” have been reported in some but not all patients. Lesions tend to be asymptomatic but itching and burning have been described. The most common extracutaneous manifestations appear to be arthralgias and arthritis. IGD usually occurs in women with rheumatoid arthritis and seronegative arthritis, but is also associated with autoimmune thyroiditis and systemic lupus erythematous.
It may also represent an adverse drug reaction with the most commonly implicated medications being calcium channel blockers, ACE inhibitors, beta-blockers, HMG-CoA reductase inhibitors, TNF-alpha inhibitors, anticonvulsants, antihistamines and anti-depressants. In addition, it may be the heralding sign for malignancy as a few case reports have found an association with acute promyelocytic leukemia, myelodysplastic syndrome, and lung cancer. The reported mean age of onset tends to be in the sixth decade of life with a female predominant ratio of 3:1.
On histopathology, palisading histiocytes surrounding foci of degenerated collagen admixed with a dense dermal interstitial infiltrate of lymphocytes, histiocytes, neutrophils and eosinophils can be seen. In IGD, the infiltrate often extends throughout the reticular dermis. However, some authors believe this is a subgroup variant of palisaded neutrophilic granulomatous dermatitis and may represent one end of the histologic spectrum. The main histological differential includes: interstitial granuloma annulare, palisaded neutrophilic granulomatous dermatitis, granulomatous drug reaction, Sweet’s syndrome and Churg-Strauss granulomatosis.
Improvement of the disorder has been reported with high-potency topical, oral, or intralesional corticosteroids, dapsone, hydroxychloroquine, cyclosporine, methotrexate, IVIG, and anti-tumor necrosis factor inhibitors. At least one study suggests that ustekinumab (Il-12 and Il-23 inhibitor) may be beneficial in severe disease that is unresponsive to multiple other treatment modalities. Additionally, spontaneous remission has also been reported. Treatment of the underlying disease may also lead to resolution of existing lesions.
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