Discussion:
Pure neuritic leprosy is an uncommon presentation of leprosy. However, in Indian subcontinent, 4.6-17.7% of leprosy patients present with nerve involvement without skin lesions [4]. Sensory, motor and/or autonomic deficit occurs along the distribution of the affected nerve.[5] Ulnar nerve and lateral popliteal nerve are the most common nerves involved in upper limbs and lower limbs respectively, though, any nerve can be involved [3].They are frequently misdiagnosed because of absence of skin lesions and negative slit skin smear and can present with Grade II disability as initial presentation [6]. Nerve biopsy is the gold standard for diagnosis but it is an invasive procedure with possible complications like nerve damage. The non-invasive high quality electrophysiological studies are helpful in the diagnosis of leprosy. [7]
On follow up, 15-35% of pure neuritic leprosy patients develop visible skin lesions which may indicate prolonged neuritic phase preceding the appearance of cutaneous lesions and most of these lesions are confirmed as borderline tuberculoid type histopathologically [8-11]. Sudden appearance of new lesions can occur due to fluctuations of cell mediated immunity in untreated or treated cases of leprosy. Some authors considered that the new skin lesions developed were possibly manifestation of reversal reaction [9-12]. Absence of visible skin lesions in patients is probably related to the deep location of granuloma in the dermis which could be manifested during reactions. This is yet to be proven. Due to absence of preexisting lesions to manifest inflammatory process, the diagnosis of type 1 reaction in pure neuric leprosy is often missed, under-recorded and under-reported [3].
In our patient, the diagnosis of pure neuritic leprosy was made by clinical examination performed by an experienced clinician combined with nerve conduction studies and the type 1 lepra reaction by increased tingling sensation with the development of edematous and erythematous new lesion over left cheek and pedal edema. This was correlated histopathologically with biopsy from these sites and resolution of pedal edema and lesion over the cheek after administration of oral corticosteroids. The clinicians should be aware about unusual presentation of type 1 reaction in pure neuritic leprosy so that unnecessary work-ups are avoided and disabilities are prevented.