Skin manifestations of systemic disease — formative SAQs

SAQ 1 (10 marks)

A 9-year-old boy is referred with three weeks of tender, warm, red nodules over both shins, a sore throat two weeks before the onset, and no other symptoms. He is afebrile and systemically well. Separately, a clinic note flags a 13-year-old girl with a velvety, dark, velvety thickening in her neck folds and axillae, a body mass index on the ninety-seventh centile, and a family history of type 2 diabetes. [1]

Question: For each child, name the cutaneous sign, state the systemic disease or risk it signals, and outline the targeted work-up and management. Explain the framework that unifies the two presentations. (10 marks) [1]

Model answer

The boy — erythema nodosum (3 marks). The tender, warm, bilateral red nodules over the shins are erythema nodosum, a reactive septal panniculitis. In a child with a recent sore throat, the commonest cause is group A streptococcal pharyngitis; the differential also includes tuberculosis, sarcoidosis, inflammatory bowel disease and drugs. The work-up is a throat swab and a rising antistreptolysin-O titre, a chest radiograph, and a tuberculin skin test or interferon-gamma release assay. Management is to treat the trigger — confirm and treat the streptococcal infection — and the nodules resolve over weeks with rest, elevation and non-steroidal anti-inflammatory drugs. They do not ulcerate or scar. [1]

The girl — acanthosis nigricans (3 marks). The velvety, hyperpigmented thickening of the neck folds and axillae is acanthosis nigricans, the cutaneous marker of insulin resistance, and in an overweight adolescent with a family history of type 2 diabetes it flags the metabolic syndrome and the risk of progression to type 2 diabetes. The work-up is a fasting glucose or an oral glucose tolerance test, a fasting lipid panel, and a glycosylated haemoglobin in the right child. Management is family-based weight management — nutrition, activity and behavioural change — because the skin improves as the insulin resistance improves, and there is no effective topical treatment for the sign itself. [3]

The unifying framework (2 marks). Both children illustrate the principle that the skin is a window to systemic disease. The framework is recognise the sign, investigate the underlying disease it points to, and refer to the right specialist — never treat the skin sign as a primary skin disease, because the lesion is a door and the systemic work-up is the room behind it. [1] [3]

Disposition (2 marks). The boy is managed as an outpatient with the targeted work-up and treatment of the streptococcal cause, and the nodules are followed to resolution. The girl is managed in the clinic with the metabolic screen and a weight-management programme, and referred to a dietitian and, if glucose intolerance is found, to paediatric endocrinology. Neither requires admission, but the recognition of the systemic link is what makes the management correct. [1] [3]

SAQ 2 (10 marks)

Question: A 10-year-old girl presents with an intensely itchy, symmetric eruption of grouped vesicles and crusts over the elbows, knees and buttocks, present for four months, with excoriation and loss of sleep. (a) What is the diagnosis and how is it confirmed? (b) Outline the management. (c) What complications and comorbidities must you address, and why is the skin sign only part of the disease? (10 marks) [6]

Model answer

(a) Diagnosis and confirmation (3 marks). The intensely pruritic, grouped vesicles on the elbows, knees and buttocks are dermatitis herpetiformis, the cutaneous face of coeliac disease. Confirm with coeliac serology — immunoglobulin A anti-tissue transglutaminase and anti-endomysial antibodies — and a duodenal biopsy while the child is on a gluten-containing diet. A skin biopsy for direct immunofluorescence of perilesional skin shows granular IgA deposition in the dermal papillae, and routine histology shows subepidermal blistering with neutrophil microabscesses. Almost every child with dermatitis herpetiformis has gluten-sensitive enteropathy, even when the gut is silent. [5] [6]

(b) Management (4 marks). The definitive treatment is a strict, lifelong gluten-free diet for the underlying coeliac disease, guided by the coeliac guideline, which clears the skin over months as the enteropathy heals. For rapid control of the itch while the diet takes effect, add dapsone, which requires screening for glucose-6-phosphate dehydrogenase deficiency and monitoring for haemolysis and methaemoglobinaemia. The skin lesions clear on the gluten-free diet, so the long-term management is dietary, not pharmacological, and dapsone is tapered and withdrawn as the diet works. Refer to a gastroenterologist and a dietitian. [5] [6]

(c) Complications, comorbidities and the skin as part of the disease (3 marks). Untreated coeliac disease carries growth failure, iron deficiency anaemia, osteoporosis and an increased risk of lymphoma, so assess growth, screen iron studies and bone density where appropriate, and set up long-term coeliac surveillance. Screen for associated autoimmune disease (thyroid disease, type 1 diabetes) and ask about a family history of coeliac disease. The skin sign is only part of the disease because dermatitis herpetiformis is the visible eruption of a systemic gluten-driven enteropathy — treating the itch alone with dapsone without the diet leaves the gut, the growth and the lymphoma risk unaddressed. The principle is the same for every cutaneous manifestation of systemic disease: the skin is a door, and the work-up is the room behind it. [5] [6]