The skin, the largest organ of the body, interacts in a complex and variable way with many other body systems. This article aims to review such interactions in relation to the GI tract.
Hepatobiliary function is a well-established cause of pruritus/prurigo and LFTs should always be included in a blood screen for pruritus. The common pruritus of pregnancy is thought likely to be secondary to subclinical cholestasis.
Figure 1: Porphyria cutanea tarda (Dr Brian Malcolm)
The porphyrias are a relatively rare inherited group of metabolic disorders, but the one most commonly encountered in the UK is porphyria cutanea tarda (figure 1), which is strongly associated with alcohol excess, but also with disorders of iron metabolism and other liver diseases, such as hepatitis.1 It manifests with fragile blisters and erosions on the dorsal aspect of the hands and fingers, healing to leave characteristic milia.
However, if the porphyria screen is subsequently normal, consider the possibility of pseudoporphyria secondary to drugs, most commonly naproxen.
Food intolerance and allergy
Food intolerance and allergy arguably have a disproportionately high profile, but there is robust evidence that they often play a part in exacerbation of atopic eczema in young children.
Current thinking is that primary sensitisation may be vectored directly through a dysfunctional epidermal barrier of perioral skin in atopic babies and infants.
A wide range of foods may be implicated in the causation of urticaria; the most common are listed in box 1. Chronic spontaneous urticaria is thought to be precipitated in some cases by chronic infection and infestation.
|BOX 1: FOODS IMPLICATED IN URTICARIAL REACTIONS|
Helicobacter pylori, the hepatitis viruses and intestinal parasites have been implicated, although in most cases, no underlying triggers are identified.
There exists a strong association between dermatitis herpetiformis (figure 2) and coeliac disease. Dermatitis herpetiformis has the reputation of being one of the most intolerably itchy of all dermatoses. Classically, the condition presents with blistering erupting on the extensor aspects of the elbows, knees, scalp and lower back. The blisters often cannot be identified because they have been disrupted by scratching.
Figure 2: Dermatitis herpetiformis (Dr Brian Malcolm)
The diagnosis should be confirmed by histology with immunofluorescence, with involved skin, preferably an intact blister, sent for standard histological analysis and perilesional non-involved skin sent for immunofluorescence. It should be remembered that patients with coeliac disease are at higher risk of developing lymphomas.
Inflammatory bowel disease
Inflammatory bowel disease can involve the skin in a number of ways. Crohn's disease can involve both ends of the GI tract, with granulomatous cheilitis of the lips (figure 3) and fissuring/ulceration of the perianal skin. It can also involve distant sites, so-called 'metastatic' Crohn's disease.
Figure 3: Granulomatous cheilitis (Dr Brian Malcolm)
Both Crohn's disease and ulcerative colitis are associated with pyoderma gangrenosum (figure 4), although this is much more common with ulcerative colitis. Pyoderma gangrenosum is essentially a clinical diagnosis, characterised by often rapid and extensive ulceration of the skin, resulting in a redundant overhanging edge and a purplish discoloration at the ulcer margin. Healing leaves scars with a cribriform appearance.
Figure 4: Pyoderma gangrenosum (Dr Brian Malcolm)
Histology can be helpful if there is diagnostic doubt, but is not pathogenic. Other conditions associated with pyoderma are rheumatoid arthritis and myeloproliferative disease.
Sweet's syndrome (acute febrile neutrophilic dermatosis) shares many characteristics with pyoderma and can often look similar. It has an association with underlying malignancies, particularly leukaemia, but also with inflammatory bowel disease and carcinomas.
The management of stomas is often complicated by contact irritant and contact allergic dermatitis, contact irritant dermatitis being by far the most common. Patch testing may sometimes be indicated if contact allergy to the components of stoma appliances, particularly adhesives, is suspected.
Peristomal dermatitis can be challenging to treat because standard topical corticosteroids can interfere with the adhesion of stoma bags. A useful alternative is a high-potency steroid inhaler, such as one containing beclomethasome, sprayed directly on to involved skin.
Cutaneous mastocytosis/urticaria pigmentosa (figure 5) can be complicated by internal mastocytomas of the liver and spleen. The diagnosis on the skin can be confirmed by eliciting Darier's sign, by gently rubbing either affected or unaffected skin, inducing a localised urticarial response. If systemic mastocytosis is suspected, blood can be taken for tryptase levels.
Figure 5: Cutaneous mastocytosis (Dr Brian Malcolm)
Osler-Weber-Rendu syndrome or hereditary haemorrhagic telangiectasia is an autosomal dominant condition affecting one in 50,000 people. Twenty per cent have no family history.
The syndrome manifests as epistaxis in children and multiple telangiectasia on the lips/oral cavity and the skin in adults, with the complications of bleeding from gut involvement.
A number of rarer conditions manifest in the skin and have an association with underlying tumours of the GI tract, both benign and malignant.
Paget's disease and extramammary Paget's disease are essentially intraepithelial adenocarcinomas, most commonly diagnosed in women in their fifties and sixties, and rare in men. Up to 25% of cases of extramammary Paget's disease will have an underlying adenocarcinoma of the bowel.2
Peutz-Jeghers syndrome is an autosomal dominant condition that manifests with multiple oral and perioral lentigines, with 40% being new mutations. There is an associated polyposis of the gut, sometimes with malignant change.3
Muir-Torre syndrome is an autosomal dominant condition that may manifest with multiple sebaceous adenomas or keratoacanthomas and a high risk of GI malignancies.
Cowden syndrome is an autosomal dominant condition in which there is an association between multiple hair follicle tumours/skin tags and GI malignancy.
Gardner syndrome is an autosomal dominant condition with an association between multiple facial epidermoid tumours and an underlying polyposis of the gut, with up to 40% risk of malignant transformation.4
A general point to bear in mind is that patients appearing to have an excessive number of skin lesions should be asked about family history of GI malignancy, because both patients and their relatives may benefit from internal endoscopic examination.
Other potential cutaneous manifestations of underlying malignancy, including those of the GI tract, are acanthosis nigricans, dermatomyositis and neurofibromatosis.
- Dr Brian Malcolm is an associate specialist and GPSI in dermatology in Barnstaple, Devon, honorary associate lecturer, Cardiff University, and committee member of the Primary Care Dermatology Society
Competing interests: None declared
1. Bonkovsky HL, Poh-Fitzpatrick M, Pimstone N et al. Porphyria cutanea tarda, hepatitis C, and HFE gene mutations in North America. Hepatology 1998; 27(6): 1661-9.
2. Yoell JH, Price WG. Paget's disease of the perianal skin with associated adenocarcinoma. Arch Dermatol 1960; 82: 986-91.
3. Giardiello FM, Welsh SB, Hamilton SR et al. Increased risk of cancer in the Peutz-Jeghers syndrome. N Engl J Med 1987; 316(24): 1511-14.
4. Gardener EJ. A genetic and clinical study of intestinal polyposis, a predisposing factor for carcinoma of the colon and rectum. Am J Hum Genet 1951; 3: 167-76.