Abstract
INTRODUCTION AND IMPORTANCE: Cydnidae pigmentation (CP) is a rare and unique pigmentation disorder caused by contact with Cydnidae bug secretions. Only 30 cases of CP have been reported to date, and this is the first case to be reported from Nepal. The unilateral involvement and resistance to alcohol wiping make this case unique, thus adding to the existing literature on CP. CASE PRESENTATION: A 21-year-old patient, student by occupation, presented with multiple hyperpigmented macules on the hand, observed upon waking during the monsoon season. The patient had no prior history of similar skin lesions or systemic symptoms. Physical examination revealed 25-30 dark brown macules on the ulnar and palmar aspect of the right hand, which were non-tender and non-itchy. The diagnosis of CP was made based on clinical presentation and seasonal timing, excluding other causes of pigmentation. Treatment involved a wait-and-watch approach, along with reassurance regarding the benign nature of the pigmentation. Follow-up at 2 weeks showed marked improvement. CLINICAL DISCUSSION: CP is often seen in rural areas during monsoon. Sudden black ink-like marks should raise suspicion of Cydnidae bug pigmentation. Management involves reassurance, as pigmentation fades naturally within 1-2 weeks. Increased awareness helps prevent misdiagnosis. CONCLUSION: The case underscores the impact of entomological and seasonal factors on dermatological conditions and highlights the importance of vigilant history taking, examination, and dermoscopy, along with considering environmental exposures in the diagnosis of rapid-onset pigmentary skin disorders.