Prurigo pigmentosa (Nagashima disease)
Last Updated: 2025-06-03
Author(s): Navarini A.A.
ICD11: -
Last Updated: 2025-06-03
Author(s): Navarini A.A.
ICD11: -
Nagashima disease, Nagashima disease, keto-rash.
Prurigo pigmentosa is a rare, inflammatory dermatosis with recurrent, very itchy, erythematous papules which heal to form a reticular post-inflammatory hyperpigmentation. Histologically, neutrophil infiltrates dominate initially, followed later by lymphocytic infiltrates with melanophages.
Originally described mainly in East Asia, increasingly also reported in Caucasian and other ethnic groups. Frequency unknown, predominantly young adults between puberty and 30 years, women more frequently affected (ratio 2-6:1). Cases are increasing worldwide due to popular ketogenic diets.
Clinically, an early stage (urticarial-papular), a full stage (papulovesicular-inflammatory) and a late stage (reticular hyperpigmentation) can be distinguished. Atypical localizations and bullous forms are rare.
The exact cause is unknown. Ketogenic conditions (diets, starvation, pregnancy, metabolic disorders) are frequent triggers. Mechanical irritation, sweating, hormonal influences and contact substances are discussed. Ketone body-induced neutrophilic inflammation is suspected.
Suddenly appearing, very itchy, erythematous papules and plaques, confluent to form net-like patterns. Papulovesicles and rarely vesicles possible. No systemic symptoms. Healing after days to weeks with characteristic reticular hyperpigmentation.
Diagnosis clinically based on typical course and morphology. Confirmation by skin biopsy with characteristic histologic picture. Direct immunofluorescence negative. Exclusion of important differential diagnoses required.
Upper back, neck and front upper trunk preferred, symmetrical distribution. Rarely face, extremities or atypical localizations. Mucous membranes, palms of hands and soles of feet are spared.
Mostly young adults with a sudden, itchy rash after a ketogenic diet or weight loss. Frequent previous unsuccessful therapy attempts with steroids or antimycotics. No general symptoms.
Early lesions: superficial, perivascular neutrophilic infiltrate, spongiotic changes, neutrophilic microabscesses. Late lesions: lichenoid lymphoplasmacellular infiltrates, pigment incontinence with melanophages. Immunofluorescence negative.
Frequently persistent post-inflammatory hyperpigmentation, cosmetically distressing. Rarely secondary infections due to excoriations. Chronic progression possible due to delayed diagnosis.
Good prognosis, disease heals quickly and completely under therapy. Recurrences possible with repeated ketosis, otherwise long-term course without complications
Avoid extreme ketogenic diets or starvation. Take care with mechanical irritation (tight clothing, rucksacks) and heavy sweating. Early dermatological clarification is advisable for symptomatic outbreaks.
Therapy of choice: Systemic administration of minocycline or doxycycline (100 mg 2× daily for 2-4 weeks), alternative therapy: Dapsone. Trigger avoidance is essential. Topical corticosteroids symptomatically helpful. In pregnancy, ketosis-avoiding measures and local therapy preferred.
