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Differentials to consider in cases of skin pigmentation include dermatological disease , including eczema and urticaria , which may result in hypo- or hyperpigmentation . Dermal melasma may also cause hyperpigmentation .
Drug-induced bluish-grey skin pigmentation may be seen in association with tetracyclines , antipsychotics such as chlorpromazine , and antimalarials . Other drugs such as NSAIDs , anticonvulsants and steroid creams may cause severe cutaneous adverse reactions , melasma and lightening of the skin respectively .
Systemic conditions to consider include Addison ’ s disease which can give the skin a ‘ muddy appearance ’, haemochromatosis which causes a grey or bronze pigmentation and polycythaemia vera causing erythema . Chronic liver disease can cause hyperpigmentation of diffuse muddy grey appearance , and hyperpigmentation may occur in association with chronic kidney disease .
Rarely , skin discolouration may be the result of exposure to heavy metal compounds such as silver ( argyria ), diffuse melanosis cutis and copper-induced discolouration of the skin .
In cases of diagnostic uncertainty , differentiation of the underlying cause can be assisted by investigations to exclude other systemic diagnoses and a skin biopsy .
Amiodarone cessation is the ideal treatment for amiodarone skin toxicity . Reducing
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amiodarone and using photoprotective cream will aid phototoxicity effects while Q-switched laser therapy is used to treat hyperpigmentation . 2 , 3 In most cases laser treatment will result in a reduction in discolouration , although some patients experience no or minimal benefit .
Treatment to consider for peripheral neuropathy induced by amiodarone include gabapentinoids such as pregabalin , tricyclic antidepressants , SSRIs and SNRIs , and magnesium supplementation . 4 Usually , low doses are required , which minimises the risk of adverse effects . Ceasing amiodarone may be of benefit , with most patients reporting recovery over 3-6 months , however some patients will have ongoing neuropathic pain despite cessation . 5
Outcome
Given the long duration of amiodarone treatment , drug dosage over that time frame , and lack of other drug or systemic causes , this is thought to be the most likely culprit . Unfortunately , Jean cannot cease or switch amiodarone due to the severity of her heart disease and side effects with alternative agents .
She is given a trial of pregabalin for hyperaesthesia , which has given her some relief from the associated discomfort .
References on request from kate . kelso @ adg . com . au
Figure 1 . Bluish discolouration of the skin of the upper limbs .
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The patient reported chronic upper limb discolouration in both limbs .
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What is the most likely diagnosis
a Palmoplantar psoriasis
b Tinea pedis
c Dry discoid eczema
d Granuloma annulare
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ANSWER The answer is b . In this case , fungal microscopy and biopsy of the lesion confirmed Trichophyton species , consistent with a dermatophyte fungal infection . Tinea pedis is most commonly caused by T . rubrum , T . interdigitale and Epidermophyton floccosum dermatophyte fungi . 1
The condition typically presents as round , scaly , asymmetrical erosions with a well-defined edge . The rash is usually more inflamed on the edge compared to the centre . The dysmorphic , yellowed toenail is also suggestive of a fungal infection . This may be caused by a variety of factors , including humidity and occlusive footwear . 2 Diagnosis is usually clinical but ideally confirmed with skin scrapings for microscopy and culture .
This patient had been incorrectly diagnosed with and treated for palmoplantar psoriasis for over two years . Palmoplantar psoriasis is characterised by scaly erythematous plaques that predominately affect the palms and soles . However , the prominent scaly edge and presence on the dorsal feet , seen in this case , is unusual for palmoplantar psoriasis . Additionally , the persistence and worsening of the rash , despite escalating treatment for psoriasis , further indicates this is not the correct diagnosis .
Discoid eczema is a common type of dermatitis that typically presents as round , erythematous , dry plaques that are mostly 1-3cm in diameter . The plaques are usually disseminated , typically including involvement of the arms and legs , and are extremely pruritic . Isolated involvement of the feet is not common . This type of dermatitis is associated with skin injury such as friction . 3 Topical steroids and UV therapy are usually effective treatment options for this condition .
Granuloma annulare is characterised by smooth , round papules and plaques . It is ring shaped and usually localised to the hands and feet . 4 Granuloma annulare is not scaly , and the centre of each ring is usually slightly depressed and clear in the middle . 5
This patient was treated with topical clotrimazole and oral itraconazole for three days , followed by topical terbinafine for three months . She was advised to keep her feet clean and dry . At review six weeks later , the rash had completely resolved . References on request from kate . kelso @ adg . com . au
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