Interstitial granulomatous dermatitis is a rare skin disorder in which there is a particular pattern of granulomatous inflammation.
The classic original clinical description of interstitial granulomatous dermatitis was of linear erythematous palpable cords on the lateral aspects of the trunk, called 'the rope sign'. However, several different types of rash have since been described with the same histological appearance.
What are the clinical features of interstitial granulomatous dermatitis?
The features of interstitial granulomatous dermatitis are variable.
Red or skin-coloured patches, papules and plaques
The shape of the lesions may be round, annular or cord-like.
Lesions wax and wane, and may vary in size and shape over days to months.
They are usually symptomless, but some patients complain of mild itch or burning sensation.
The lesions tend to be symmetrically distributed on the trunk, but proximal limbs may also be affected.
Dense histiocytic inflammation in the reticular (lower) dermis
Sparse neutrophils and eosinophils
Perivascular and interstitial lymphocytes
Interstitial histiocytes (between the collagen bundles) or palisaded histiocytes (lined up perpendicular to fragmented central collagen).
Focal degeneration of collagen, which may be surrounded by space (floating sign)
Few giant cells.
How does interstitial granulomatous dermatitis compare to granuloma annulare?
Granuloma annulare and interstitial granulomatous dermatitis may appear similar clinically and histologically.Granuloma annulare also presents with papules and plaques, but these are typically on the back of the hands or feet, whereas the trunk is a more common site for interstitial granulomatous dermatitis. Granuloma annulare is less often associated with autoimmune diseases.
Several different types of rash have been described with the same histological appearance including annular plaques on the trunk. Lesions are often tender and may ulcerate.
How is palisading neutrophilic granulomatous dermatitis diagnosed?
Palisading neutrophilic granulomatous dermatitis is diagnosed on skin biopsy. The characteristic histological features of palisading neutrophilic granulomatous dermatitis are:
Intense neutrophilic infiltrate and nuclear dust
Interstitial histiocytic infiltrate
Collagen degeneration
Leukocytoclasticvasculitis
Variable histological appearance depending on the stage of the eruption.
Palisading granulomas seen have also been described as miniature ‘Churg-Strauss granulomas’ or flame figures, with degenerated collagen enveloped by eosinophils resembling a flame. Flame figures are also seen in the pathology of Wells syndrome.
What are the clinical associations of granulomatous dermatitis?
Several conditions have been noted to arise in association with interstitial granulomatous dermatitis. There is less information about associations with palisading neutrophilic granulomatous dermatitis.
Autoimmune diseases and conditions
Both forms of granulomatous dermatitis have often arisen in people with other conditions considered autoimmune in origin, implying an immune-complex mechanism may be involved in the pathogenesis [2]. These have included the following conditions.
Rheumatoid and non-rheumatoid arthritis, characteristically symmetrical and involving the fingers, wrists, elbows, and shoulders, is the most common association. Arthritis (inflamed joints) or arthralgias (painful joints) may occur before, during or years after the onset of the skin lesions in about 50% of published cases of interstitial granulomatous dermatitis [3].
In a literature review of 15 patients with interstitial granulomatous dermatitis, autoantibodies identified on blood testing included rheumatoid factor (RhF), antinuclear factor (ANA), thyroglobulin, SS-A Histone, DNA histone and ANCA [4].
Malignancy
There are some reports of association of malignancy with interstitial granulomatous dermatitis. In one case, the lesions cleared after lung cancer was treated [5]. Rare associations of granulomatous dermatitis with leukaemia [6], lymphoma, breast cancer, hypopharyngeal squamous cell carcinoma and endometrial neoplasia have been reported.
How is granulomatous dermatitis treated?
Granulomatous dermatitis typically flares and remits. Successful treatments have included:
One case associated with SLE responded well to systemic steroids after 15 days [2].
Although tumournecrosis factor (TNF)-alpha inhibitors have been recently described as inducing interstitial granulomatous dermatitis [7], etanercept has been used in interstitial granulomatous dermatitis associated with rheumatoid arthritis with complete skin clearance and improvement in arthritis [8].
Interstitial granulomatous drug reaction
Interstitial granulomatous dermatitis induced by medications is known as an interstitial granulomatous drug reaction. It is thought to be a distinct clinical and pathological entity. It presents as annular plaques, and nodules on the trunk, arms, medial thighs and skin folds. The rash resolves when the responsible drug is withdrawn.
How is an interstitial granulomatous drug reaction diagnosed?
Interstitial granulomatous drug reaction is diagnosed by skin biopsy. The characteristic histological features of interstitial granulomatous drug reaction are:
Basalepidermal cell vacuolisation
Lichenoid changes with eosinophils
Absence of neutrophils
In some cases, palisaded granulomatous changes associated with collagen necrosis and floating sign.
Medications that have been reported to be implicated in interstitial granulomatous drug eruption include:
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Deng A, Harvey V, Sina B, Strobel D, Badros A et al. Interstitial granulomatous dermatitis associated with the use of tumor necrosis factor alpha inhibitors. Arch Dermatol. 2006; 142: 198–202. PubMed
Zoli A, Massi G, Pinnelli M, Cuccio C, Castri F et al. Interstitial granulomatous dermatitis in rheumatoid arthritis responsive to etanercept. Clin Rheumatol (2010); 29: 99–101. PubMed