Pyoderma Gangrenosum

Pyoderma gangrenosum is a destructive necrotising non-infective ulceration of the skin. It is associated with:
1. Gastrointestinal disease e.g. ulcerative colitis, Crohn's disease
2. Hepatic disease e.g. chronic active hepatitis, primary biliary cirrhosis, sclerosing cholangitis
3. Joint disease e.g. rheumatoid arthritis, seronegative arthritis
4. Haematological disease e.g. leukaemias, lymphoma, monoclonal gammopathies
5. Neoplasia e.g. carcinoma of breast, bronchus, colon
6. Others such as infections, diabetes, thyroid disease, lupus erythematosus.

Dermatomyositis

Dermatomyositis (DM) clasically presents with a periorbital heliotrope rash, but at times the purple discoloration is not seen and the diagnosis of DM is one to consider in a patient with periorbital oedema. The finding of erythematous papules over the knuckes (Gottren's papules), linear erythema along the dorsal surface of the fingers, and ragged, erythematous nailfolds indicates DM.

There is often a detectable proximal myopathy and patients will struggle with activities that involve lifting their arms above the shoulders, as in this case. There is an association with malignancy, particularly lung and upper aerodigective tract. The patient's cough suggests he may have an underlying lung cancer.

Differential

Hypothyroidism can cause periorbital oedema and a proximal myopathy but doesn't explain the rash.

PAN often presents with middle aged men and could explain his cough but causes myalgia and a vasculitic rash.

Rash

Polymorphic light eruption is a common photosensitivity disorder which particularly affects young females. The skin shows 'hardening', such that areas frequently exposed to the sun, such as the face and hands, may not be affected whilst newly exposed sites are most severely affected. The rash often develops after a few days of sun exposure and is most severe at the beginning of the summer and improves at the end of the summer as the skin 'hardens'.

Systemic lupus erythematosus is a photoaggravated disorder in which the face is usually affected.

Photoallergic contact dermatitis can occur due to sunscreen allergy. A rash would appear at all sites where sunscreen had been applied and subsequently exposed to the sun.

Scabies is not photoaggavated.

Patients with xeroderma pigmentosum describe easy burning after minimal sun exposure. They subsequently develop freckling, chronic solar damage and skin tumours.

Chickenpox, which is clearly very much the more common disease, causes a rash which crops, is typically central, and does not affect the hands and feet.

Smallpox rash is more distal and causes deep lesions which leave scars (typically on the face).

Contact dermatitis caused by allergy to eye make-up

Her erythematous, scaly, lichenified eyelids were due to contact dermatitis caused by allergy to the eye make-up she had been using.

Atopic eczema could produce a rash on the eyelids like this, but not in isolation. Look in particular for a history of atopy and involvement of the limb flexures when considering this diagnosis.

Systemic lupus erythematosus characteristically causes a photosensitive rash, which would spare the upper eyelid and not affect it.

Drug-induced rash

Purpura in the context of a drug reaction may be an isolated skin reaction, or it may be a manifestation of drug-induced thrombocytopenia or drug-induced vasculitis. Hydralazine is associated with drug-induced lupus-like syndrome that can present with a vasculitic purpuric rash. Systemic features such as fever, malaise and arthralgia may be present, and other organs including the liver, kidney and heart may be affected. Anti-histone antibodies may also be present. The drug should be stopped immediately and systemic corticosteroids may be of benefit. Other drugs associated with a purpuric skin rash include aspirin, sulphonamides, penicillin, thiazides, furosemide and corticosteroids.

Tests used in Atopic Dermatitis

Total IgE titre does show some correlation with disease activity and it can be a useful screening tool in patients in whom a diagnosis of atopic dermatitis is being considered. Positive radioallergenosorbent (RAST) tests to foods such as nut, wheat and milk are rare in patients with atopic dermatitis, but in Northern European affected adults there are positive RAST tests to:
▪ house dust mite in 50-60%
▪ cat dander in 50%
▪ grass in 75%
▪ birch pollen in 65%.
There is generally a good correlation between skin prick test reactivity and RAST test to these allergens.

Prick tests involve the intradermal injection of allergen with assessment of the immediate urticarial reaction and are believed to reflect type I allergic reactions. In contrast patch tests involve applying antigen to the skin for 48 hours and assessing the subsequent delayed eczematous reaction. This is believed to more closely reflect type IV delayed hypersensitivity reactions and is used clinically to investigate patients with suspected contact allergic dermatitis to environmental antigens such as nickel.

Alopecia

The two most common causes of scarring alopecia are lichenplanopilaris (lichen planus affecting the scalp hair follicles) and discoid lupus erythematosus. Both conditions cause inflammation, and can be difficult to differentiate clinically.

Androgenetic alopecia and Alopecia areata are both non-scarring causes of alopecia.

Traction alopecia can cause scarring but is not usually associated with inflammation. Alopecia occurs at sites of traction and is usually caused by hair styling practices, such as braiding.

Common Drug Side Effects

mouth ulcers and methotexate

striae and steroids

argyria and silver-based preparations

hair loss and oral contraceptive

erythema multiforme and ampicillin.