Observing the skin: Papules and nodules in leprosy

In reports of clinical cases of leprosy one can read: ‘presence of papules and nodules or papulo-nodular lesions’. In a leprosy patient there can be present either papules or nodules but not these two elementary lesions together. It is reported in books of dermatology that: “papule is a solid elevated lesion up to 1 cm of diameter”. It is also reported: “papules are usually caused by an infiltrate within the papillary dermis”. Nodule is described as “a round elevated lesion greater than 1 cm in diameter” and that “nodules usually result from relatively massive infiltrates in the dermis, but they can also arise from large infiltrates in the subcutaneous fat”. In practice these two elevated lesions are differentiated by their size but this may be misleading. There are small nodules with the same dimension of the papules. The sizes we appreciate clinically do not always correspond to the underlying different histological patterns that differentiate between papule and nodule. In leprosy to differentiate between papule and nodule is important. The papules show an infiltrate that is ‘pressing’ against the epidermis; they are seen in the hyperergic paucibacillary forms of leprosy (TT, BT) and they are not symmetrically distributed. The nodules show an infiltrate at full thickness in the dermis without involving the epidermis; they are seen in the hypo or anergic multibacillary forms of the disease (BL, LL) and have a symmetrical distribution. Therefore in leprosy small and big nodules may be observed together but papules and nodules may not. If papules and nodules were described on the same patient, the diagnosis of leprosy could be questioned. There are only anecdotal reports of few cases of LL leprosy presenting with one nodule.