Lyme disease misdiagnosed as psoriatic arthritis
In their article, “Rare case of Lyme borreliosis in a patient presenting with dactylitis and skin rash,” Steppat et al. describe a patient with Lyme borreliosis, who was initially misdiagnosed with Psoriatic arthritis (PsA), a chronic inflammatory disease that occurs when your immune system mistakenly attacks healthy joints and skin. 
The man, in his 70’s, presented with dactylitis (severe swelling of the fingers or toes), onycholysis of the nails (nail separates from the skin) and scalp psoriasis, which lead to the diagnosis of psoriatic arthritis.
However, he did not respond to treatment with corticosteroids or disease-modifying antirheumatic drugs.
“A skin biopsy was performed showing histopathological changes compatible with Lyme borreliosis (LB) and serum contained IgG antibodies against Borrelia burgdorferi,” wrote Steppat and colleagues.
“To our knowledge, this is the first case of LB describing asymmetrical dactylitis in a hand.”
The man did not recall a tick bite but reported that his fingers first began to swell several weeks after gardening.
“It was concluded that the patient was not suffering from PsA but [Lyme borreliosis] with manifestations of dactylitis, arthritis and [acrodermatitis chronica atrophicans] ACA,” the authors wrote.
After 1 week of penicillin, the swelling of the patient’s fingers improved.
After 6 months, the arthritis, tenosynovitis (inflammation of the tendon sheath), soft tissue swelling and skin rash had completely resolved.
“… dactylitis is a common feature of [psoriatic arthritis]. However, dactylitis may also be seen as a clinical feature in several other diseases such as [Lyme borreliosis].”
Furthermore, the authors point out, that Lyme borreliosis can occur even when there is no history of a tick bite or erythema migrans rash.
When a patient is not responding to treatment for psoriatic arthritis, it is “crucial to re-evaluate the medical history, objective examinations and laboratory tests. In this case, the conclusive clue was hidden in the skin biopsy.”
- Steppat A, Skaarup Andersen N, Andreasen CMRare case of Lyme borreliosis in a patient presenting with dactylitis and skin rashBMJ Case Reports CP 2023;16:e253182.