Papulosquamous Disorders — Practice

Question 1

Pinpoint bleeding after removal of scale from a psoriatic plaque is called

Accepted Answer

B

Question 2

The fine white lacy lines on the surface of a lichen planus papule are

Accepted Answer

B

Question 3

A 24-year-old develops a shower of small scaly papules over the trunk two weeks after a sore throat. Both parents have psoriasis. Diagnosis and management?

Accepted Answer

Guttate psoriasis precipitated by streptococcal pharyngitis. Drop-like lesions appearing over days in a young person after a throat infection, with a family history, is the classic presentation.

Confirm the trigger with a throat swab and antistreptolysin O titre and treat active infection. The eruption often resolves over weeks to months, and narrowband ultraviolet B phototherapy is useful for extensive disease. A substantial proportion later develop chronic plaque psoriasis, which is worth saying honestly. Systemic corticosteroid must be avoided, since withdrawal can precipitate generalised pustular psoriasis.

Question 4

A 45-year-old has itchy violaceous flat-topped papules on the flexor wrists with fine white surface lines, and a lacy white pattern on the buccal mucosa. Diagnosis, and what two things would you check?

Accepted Answer

Lichen planus, showing the six Ps with Wickham striae and characteristic oral involvement.

First, check hepatitis C serology, since the association is well described and testing is reasonable in patients with oral or extensive disease.

Second, check the drug history. A lichenoid drug eruption can be clinically and histologically similar, with antihypertensives, antimalarials and antituberculous drugs among recognised culprits, so identifying one avoids immunosuppressing a drug reaction. Erosive oral disease additionally requires long-term follow-up because of a small risk of squamous carcinoma.

Question 5

A hairdresser develops an itchy vesicular eruption on the hands and later on the eyelids. Distinguish the two types of contact dermatitis and state which test is appropriate.

Accepted Answer

Irritant contact dermatitis is direct chemical damage to the skin, requires no prior sensitisation, occurs in anyone given sufficient exposure, and is confined to the area of contact, which in a hairdresser typically means the hands from frequent wetting and detergents.

Allergic contact dermatitis is a type IV delayed cell-mediated hypersensitivity requiring prior sensitisation, affects only sensitised individuals, and characteristically spreads beyond the contact site, which is why eyelid involvement from a hand-applied allergen is typical. Paraphenylenediamine in hair dye is a common culprit.

Patch testing is the correct investigation, applied for 48 hours with readings at 48 and 96 hours. Prick testing detects IgE-mediated immediate hypersensitivity and is the wrong test for this mechanism.

Question 6

A patient with extensive plaque psoriasis is given oral prednisolone with rapid improvement. Two weeks after the course ends he develops widespread sterile pustules, fever and malaise. Explain.

Accepted Answer

Generalised pustular psoriasis precipitated by systemic corticosteroid withdrawal.

Systemic steroid suppresses psoriasis dramatically, which is precisely why it is tempting to prescribe, but withdrawal produces a rebound that can convert stable plaque disease into a life-threatening pustular form. The pustules are sterile, representing neutrophil accumulation rather than infection.

Generalised pustular psoriasis is a medical emergency with fever, systemic upset, hypoalbuminaemia, electrolyte disturbance and a risk of sepsis and cardiovascular collapse, and it requires admission with supportive care alongside specific therapy such as acitretin, ciclosporin or a biologic.

This is the reason systemic corticosteroids are avoided in psoriasis altogether, and it is one of the most reliably examined pieces of prescribing knowledge in dermatology.

Question 7

A 68-year-old man has had generalised red scaly skin for four months with itch, having failed treatment for presumed eczema. Give the diagnostic category, the immediate concerns and what must be excluded.

Accepted Answer

This is erythroderma, defined as inflammation of more than about 90 per cent of the body surface, and it is a dermatological emergency in its own right regardless of cause.

The immediate concerns are physiological. Massive cutaneous vasodilatation produces high-output cardiac failure and heat loss with hypothermia, extensive scaling causes protein and fluid loss, and barrier failure invites infection. Management therefore begins with warmth, fluid and protein replacement, emollients and treatment of infection before any cause-specific therapy.

What must be excluded is cutaneous T cell lymphoma, particularly given his age and the failure of treatment for a presumed benign cause. Early histology in mycosis fungoides and Sezary syndrome is frequently non-specific, so repeated biopsies over time, with immunophenotyping and T cell receptor gene rearrangement studies, are often required before the diagnosis is secure.

Question 8

Explain why psoriasis produces pinpoint bleeding when scale is removed while lichen planus does not.

Accepted Answer

Because the two diseases damage different parts of the epidermis and remodel the dermal papillae differently.

In psoriasis, keratinocyte turnover accelerates so that epidermal transit time falls from around 28 days to about four. Rete ridges elongate regularly, the dermal papillae become tall with dilated tortuous capillaries, and the epidermis directly above those papillae becomes thinned. Removing the adherent scale therefore strips a very thin layer over dilated superficial vessels, which bleed at discrete points corresponding to individual papillae. That is the Auspitz sign.

In lichen planus the attack is on basal keratinocytes, and the surface response is hyperkeratosis with wedge-shaped hypergranulosis rather than parakeratosis. There is no suprapapillary thinning and no papillary capillary dilatation, so the scale is compact and adherent and its removal exposes no vessels. The visible surface change is instead Wickham striae, the thickened granular layer seen through the surface.

Question 9

A 22-year-old has a widespread oval scaly eruption on the trunk. A colleague diagnoses pityriasis rosea and offers reassurance. What must be checked before accepting this?

Accepted Answer

Secondary syphilis must be excluded, because it can produce an almost identical eruption and the consequences of missing it are serious.

Three features separate them. Pityriasis rosea characteristically begins with a single herald patch one to two weeks before the shower of smaller lesions, and its absence should raise doubt. Secondary syphilis characteristically involves the palms and soles, which pityriasis rosea spares. And secondary syphilis is accompanied by generalised lymphadenopathy, often with mucous patches, condylomata lata and constitutional symptoms.

Serological testing settles the question inexpensively. It is also worth confirming that the lesions align along cleavage lines with an inward-facing collarette of scale, and that a drug history does not suggest a pityriasiform drug eruption. If the diagnosis is genuinely pityriasis rosea, telling the patient it will take six to eight weeks to clear prevents a series of anxious return visits.

Practice — Papulosquamous Disorders

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